American Welding Society Welding Symbols: The Complete Guide

A fabricator I once read about cut forty steel gussets exactly to print, tacked them into a frame, and only then realized the welder had put every bead on the wrong side of the joint — a simple arrow side mistake that cost a full shift of grinding and rework. Welding symbols are the shorthand that prevents that scene, and once you can read them fluently, every drawing in front of you starts talking.

Why American Welding Society Welding Symbols Matter on Every Drawing

Imagine an entire crew of fitters cutting and tacking dozens of heavy steel gussets to a structural frame. Every measurement was double checked, every part was cut exactly to print, and the job was right on schedule. The only problem is that once the welders begin laying their beads, an inspector catches it: every one of those critical welds was placed on the opposite side of the joint from what the drawing intended. Now, instead of moving onto the next assembly, the crew is stuck grinding out near perfect welds and redoing them from scratch. This is the exact kind of avoidable, costly mistake that American Welding Society welding symbols were made to prevent.

At its core, an AWS welding symbol is a universal shorthand used on engineering and fabrication drawings to specify welding, brazing, and nondestructive examination information by means of symbols. Rather than writing out a paragraph that reads, “weld a 5/16 inch fillet on the arrow side of this T-joint for the full length,” a drafter can communicate every one of those instructions in one compact symbol. According to AWS A2.4, these symbols are defined as a method of specifying this information with detailed illustrations and examples for the purpose of construction and interpretation. Simply put, the goal isn’t to make drawings look complicated, it’s to make them unambiguous.

A Language For The Entire Shop

The beauty of this system is that it isn’t made for just one person. It is a shared language between the people that make up a fabrication shop. For welders, it tells them exactly what type of weld to make, where to make it, and how large it needs to be. For fitters, it helps them prepare joints correctly before any arc is struck. For inspectors, it gives them an objective, standardized checklist to hold the final product to. For students, it is one of the first skills that bridges the gap from classroom theory to the shop floor. Lastly, for engineers, it allows them to convey their design intent without having to cram long written instructions onto every single joint.

This level of communication becomes even more crucial when working with specialized jobs, such as intricate repairs covered within an alloy wheel welding guide, or structural builds where precision is non-negotiable. No matter the material, if the joint is on a print, there is a good chance it is relayed through these symbols.

The Standard That Keeps It Consistent

For this language to be universal across the United States, it needs one governing standard. That standard is AWS A2.4, published by the American Welding Society, which is headquartered in Miami, Florida. It is an American National Standard that has been approved by ANSI. Its lineage can be traced all the way back, with AWS A2.4:2020 being its 8th edition, superseding AWS A2.4:2012. This edition continues to standardize the method of relaying welding, brazing, and nondestructive examination information for construction and interpretation. Resources such as the AWS Welding Symbol Chart are built directly off of this standard, keeping shops consistent from one job to the next.

The Scope of This Guide

With that being said, the goal of this article is purely informational. Over the course of the sections to follow, this guide will break down exactly what these symbols mean, how they are structured, and how they are read step by step. From the location of the arrow, all the way down to dimensions and supplemental notes, each piece has a purpose. Furthermore, it will cover the key differences between the American system and international variants, such as ISO 2553, as these can be the source of confusion on globally sourced prints.

Learning to read American Welding Society welding symbols is not a party trick for a welder, it’s insurance against rework. One misplaced weld can devour an entire shift, but one second of properly reading a symbol can prevent it all. With the standard set in place and the language to learn, every drawing that crosses a shop bench can be read for exactly what it is: a precise set of instructions, with no room for guesswork.

The Standard Behind the Symbols: What AWS A2.4 Actually Is

Before you memorize a single glyph, it helps to know where the language came from. Every American fabrication drawing you will ever read is written in a dialect defined by one document: ANSI/AWS A2.4, Symbols for Welding, Brazing, and Nondestructive Examination. Knowing its history explains a lot of shop-floor confusion, including why two competent shops can annotate the same joint slightly differently.

Two Older Standards That Merged Into One

The story starts with two separate documents. AWS A2.0, Standard Welding Symbols, was first published in 1947 and revised in 1958 and again in 1968. AWS A2.2, Nondestructive Testing Symbols, first appeared in 1958 and was revised in 1969. Neither was written in isolation. Both grew out of joint work between the American Welding Society and the American Standards Association Sectional Committee Y32, the committee that coordinated drawing and engineering graphing standards in the United States.

By the mid-1970s it made little sense to keep two symbol vocabularies on the same print, so in 1976 A2.0 and A2.2 were combined and superseded by a single standard: AWS A2.4. Because the work was processed through ANSI, the document carries the ANSI/AWS designation. One standard now covers welding symbols, brazing symbols, and the examination symbols that inspectors depend on.

Edition Lineage Through 2020

The standard has been revised on a fairly steady cycle since it was created. The recognized sequence runs:

• ANSI/AWS A2.4-76, the first edition, merging A2.0 and A2.2
• ANSI/AWS A2.4-79, -86, -93 and -98
• A2.4:2007, A2.4:2012, and the current A2.4:2020

The year after the colon matters more than most beginners expect. A drawing annotated under the 1998 edition can carry notations that were retired later. The 2020 revision dropped the old flash and upset symbols in favor of writing FW or UW in the tail, removed the diameter symbol from the plug symbol, and limited flat contour to fillet welds. If a print and your symbol chart disagree, check the edition before you assume either one is wrong. The official AWS A2.4:2020 preview is the quickest way to confirm current practice.

What the Standard Actually Covers

A2.4 defines three symbol families: welding symbols for fusion welding, brazing symbols for brazing, soldering and braze welding, and nondestructive examination symbols used to call out radiography, ultrasonic testing and similar methods. It also fixes the anatomy of the symbol itself: the reference line, the arrow, the tail, the basic weld symbols, the supplementary symbols, and the standard location of every dimension.

What A2.4 does not do is tell you how to weld. Quality, acceptance criteria and procedure qualification live in other documents. Structural shops work to AWS D1.1, pressure vessel work follows the ASME Boiler and Pressure Vessel Code, and highly regulated sectors such as aerospace layer on their own requirements, which our overview of Aerospace Welding: Processes, Standards, and Careers Guide walks through. The same split shows up in process selection: A2.4 lets you write FCAW in a tail, but deciding whether Aluminum Flux Core Welding: What Actually Works in 2026 is the right call for your joint is a procedure question, not a symbol question. In short, A2.4 supplies the vocabulary; the code supplies the rules of quality.

A Voluntary Consensus Standard, Not a Law

It is worth being precise about what “standard” means here. A2.4 is a voluntary consensus standard developed under ANSI’s due process rules: a balanced committee of welders, engineers, educators, inspectors, fabricators and producers reviews proposals, comments and ballots before text is approved. No government agency compels anyone to use it. It becomes mandatory only when a contract, a specification, or a governing code adopts it by reference, which is exactly what happens on most American structural and pressure-retention work.

That also means the symbols are not proprietary AWS property in any practical sense. The system is widely reproduced, taught and referenced, and you will find the same glyph shapes in textbooks, on free charts, and inside CAD and CAM annotation toolbars. Learning it is learning a trade-wide language, not one company’s shorthand.

Weld Symbol vs. Welding Symbol: The Distinction That Shows Up on Tests

Two terms sound interchangeable and are not. A weld symbol is the specific glyph that indicates the type of weld, such as the fillet triangle or the single-V. A welding symbol is the complete assembly on the drawing: the reference line, the arrow, the weld symbol itself, and any dimensions, supplementary symbols or tail notation that travel with it.

That is why a print can carry a perfectly valid welding symbol with no weld type at all, and why exam questions love to trap people with “which of these is required?” The reference line and arrow are the skeleton; the weld symbol is just one organ hung on it. Once this distinction clicks, the anatomy in the next section becomes far easier to read, because you stop looking for a single picture and start reading a structured, layered instruction. The free AWS welding symbol chart lays out that structure in one page and is worth printing before you move on.

Anatomy of a Welding Symbol: Reference Line, Arrow, Tail and Dimensions

Every American Welding Society welding symbol is built from a small, fixed kit of parts. Once you know what each part does, a dense fabrication drawing stops looking like hieroglyphics and starts reading like a set of instructions. AWS A2.4 lays out that kit as a standardized grammar: a line to write on, an arrow to aim it, an optional tail for references, and dimension slots that never move. Learn the anatomy once and every symbol you meet afterward is just a variation of the same skeleton.

The Reference Line and the Arrow: The Only Two Required Elements

Two parts are mandatory. Everything else is optional.

The reference line is the horizontal line that anchors the symbol. All welding information is attached to it, either above it or below it, and that placement is never decorative. The side of the line a symbol sits on is what tells the welder which side of the joint to weld. The reference line also carries the supplementary marks: the all-around circle at the arrow junction, the field weld flag at the arrow end, and contour or finish marks above or below the weld symbol itself.

The arrow connects the reference line to the joint on the drawing. AWS is picky about where it lands: the arrow must point to a line on the drawing that conclusively identifies the proposed joint, preferably a solid object line rather than a hidden line, center line, or a vague gap between parts. A fuzzy arrow location is one of the quiet ways drawings go wrong, because if the joint itself is ambiguous, the side rules downstream have nothing to attach to.

The basic weld symbol (the little V, arrow-tail, fillet triangle, and so on) and any supplementary symbols hang off the reference line. Section five of this guide walks the full library; here, the important point is that the weld symbol is a placeholder that gains meaning only from its position on the line and from the dimensions around it.

The Tail: Where Specifications and Processes Live

The forked tail at the end of the reference line is not required. It is simply omitted when no additional reference is needed. When it appears, it carries the specification, process, or other reference for the joint: a process acronym such as SMAW, GMAW, or FCAW, an acceptance standard, a welding procedure specification number, or a detail drawing callout. So a tail reading GMAW is telling you the process without cluttering the dimension zones, which is handy on drawings where a fabricator might otherwise have to cross-reference a note block. The same logic applies when the tail names a process covered elsewhere, whether that is routine carbon steel work or something more specialized such as Alloy Steel Welding Electrodes: Selection, Use & Safety.

The Standard Location of Every Dimension

Dimensions occupy fixed slots, and those slots do not change with the arrow’s direction or the weld type. The official AWS weld symbol chart maps them like this:

Element	Standard location
Weld size, effective throat, or strength	Left of the weld symbol
Depth of bevel, groove angle, root opening	Left of the weld symbol, stacked in a set order
Length of weld and pitch (spacing)	Right of the weld symbol
Number of welds in a group	Above the weld symbol
Depth of filling for plug and slot welds	Above the weld symbol
Contour (flush, convex, concave) and finish designator	Directly above or below the weld symbol
Weld-all-around circle	At the junction of reference line and arrow
Field weld flag	Top of the reference line at the arrow end
Specification, process, or reference	Inside the tail

The practical takeaway is the left-right split: size information lives to the left, length and spacing live to the right. Because that split is fixed, you can read a symbol at a glance even when the arrow points up, down, or back to the left.

Reading Order: Left to Right, Top to Bottom

Information on the reference line is always read left to right and top to bottom, regardless of how the arrow is oriented. This is the rule beginners most often break. When an arrow points leftward, the temptation is to start at the arrow end and work backwards. Don’t. The reference line has a fixed reading direction; only the arrow rotates. Think of it as a sentence: you read from the start of the line toward the tail, no matter which way the line is aiming on the page.

A good habit is to sketch the reference line yourself when you are checking someone else’s drawing. Draw the horizontal line, mark the arrow, then fill in symbol, dimensions left, length and pitch right, supplementary marks, and tail last. The AWS A2.4 standard and practical reading guides both present the anatomy in this order, and practicing it in sequence builds the muscle memory that prevents misreads under shop pressure. Once the parts are automatic, the next question is simply which side the arrow is talking about.

Arrow Side vs Other Side: The Rule That Prevents Rework

When reading any print that utilizes the American Welding Society welding symbols, the most important location rule to remember is the difference between the “arrow side” and the “other side”. This simple placement determines exactly which side of a joint will receive the weld, and overlooking it is one of the leading causes of costly rework in the shop. By fully understanding this rule, fabricators can eliminate the guesswork that leads to misplaced beads.

The Foundation: Which Side is Which?

The arrow side is the side of the joint to which the arrow points. Conversely, the other side is the side opposite the arrow side. While this may sound straightforward, the direction that the arrow is drawn (up, down, left, or right) does not change these sides at all. This is a staple rule of AWS A2.4 that is practiced throughout a multitude of trades, from structural steel to aerospace TIG welding.

To translate this onto the reference line, AWS utilizes a strict placement rule: arrow-side weld symbols are placed below the reference line, and other-side weld symbols are placed above the reference line, regardless of the arrow’s direction. If a symbol is shown on both sides of the reference line, it indicates that identical welds are required on both the arrow side and the other side of the joint. This placement consistency allows welders to read a symbol in an instant without having to rotate their thought process with every drawing.

Breaking the Arrow: Identifying the Prepared Member

For many groove welds, only one member of a joint is required to be beveled prior to welding. To clearly indicate this, AWS utilizes a break in the arrow. A break in the arrow is used to identify the member of the joint to be prepared, such as the member receiving the bevel for a single-bevel groove weld. The side of the joint that the broken arrow points toward is the member that is to be shaped, not necessarily the side that receives the entire weld.

This specification is incredibly important to prevent over-prepping parts or prepping the incorrect member. Many shops utilize aluminum cleaner for welding and precision machining to prep joints, making the arrow break a crucial instruction to follow. For a full breakdown of these groove designations, AWS provides a welding symbol chart to reference in the shop.

Multiple Lines and Multiple Arrows

Not every joint is completed in a single pass. For assemblies that require multiple weld operations, multiple reference lines are utilized. The rule for sequencing is simple: the line closest to the arrow is performed first, followed by the next line outward, and so on. This allows engineers to designate the order of operations without cluttering the print with notes.

Additionally, some drawings will feature multiple arrow lines extending from the same reference line. These arrows are used to apply the same welding symbol to multiple joints on the print. When this occurs, each arrow is read independently based off of the joint that it points to. These features are commonly seen on large fabrications, such as those taught within an aluminium welding course, where repeatability across parts is vital.

The Five Basic Joint Types

With the arrow side rules established, they can now be applied to the five joints that AWS identifies. These five basic joint types are: butt, corner, T, lap, and edge joints. Each of these joints utilizes the arrow to dictate location:

Joint Type	How the Arrow Applies
Butt	Arrow points to the junction between two members in the same plane.
Corner	Arrow points to the outside corner where two members meet at an angle.
T	Arrow points to the intersection of the stem and the base member.
Lap	Arrow points to the overlap between the two lapped pieces.
Edge	Arrow points to the edge contact between the parallel members.

Whether you are working on aluminum boat welding or heavy structural builds, applying these location rules to these joints will ensure that your welds are placed exactly as specified.

The Basic Weld Symbol Library: Groove, Fillet, Plug, Slot and More

Every welding symbol you will ever read is built from a surprisingly small alphabet. AWS A2.4 defines a set of basic weld symbols, each a little glyph standing for a specific weld type, and the system works because the same glyph means the same thing on any drawing. Learn the library once and you can decode groove details on a pressure vessel sketch, a chassis jig print, or a field sketch without looking anything up.

The best reference for this section is the official AWS welding symbol chart, which lays out every basic symbol alongside its supplementary marks. Keep a copy taped inside your toolbox lid.

Groove Weld Symbols

Groove welds describe joints where the edges of the members themselves are prepared, so their symbols are drawn to mimic the shape of the joint. AWS recognizes six: square groove, V-groove, bevel groove, U-groove, flare-V groove and flare-bevel groove.

The first four depend on edge preparation you can see on the print. A square groove means plain sheared or flame-cut edges butted together. A V-groove means both members are beveled to form a V. A bevel groove means only one member is beveled, which is why that symbol pairs with the break in the arrow discussed later. A U-groove means a machined radius, used on heavy sections where a U profile deposits less weld metal than a deep V.

Flare grooves are different: nobody cuts them. They occur naturally where a rounded or rolled surface meets a flat one, like the toe of a rolled beam, a pipe edge, or a formed sheet corner. Because the joint geometry is inherited rather than prepared, the 2020 edition of A2.4 added detailed usage and sizing guidance for flare groove welds. AWS A2.4:2020 covers this directly, and the change is summarized in the ANSI analysis of the 2020 revision.

All six carry arrow side, other side, and both sides significance. That matters: the glyph sits below the reference line when the groove is on the side the arrow points to, above it when it is on the far side, and on both lines when both members are prepared.

Fillet, Plug and Slot

The fillet symbol is a right triangle, probably the most common symbol you will see. Fillets join two surfaces at an angle, typically in T-joints, corner joints, and lap joints, and they carry arrow side, other side, and both sides significance. The triangle below the line and above it in one symbol means a fillet weld on both sides. The size number sits left of the triangle; leg versus throat is covered in the dimensions section.

Plug and slot welds use a symbol that looks like an open rectangle with one square end. Both describe welds deposited inside a hole or elongated slot punched or cut in one member, fusing it to the member behind; both carry arrow side, other side, and both sides significance. You will meet them on sheet metal lap joints, base plates, and tubular connections where a row of plug welds replaces bolts. A boat builder stitching a reinforcement plate to hull plating with a staggered line of plug welds is the kind of joint where an aluminum boat welding drawing calls for the plug symbol plus a depth-of-filling note.

Spot, Seam, Projection and Stud

Resistance and fastener welds get their own family: spot (a circle), seam (a circle with two vertical tails), projection (a circle with a bar), and stud (an inverted T with a circle). The rule that trips people up: these four carry no arrow side or other side significance. The symbol sits on the reference line regardless of which side the arrow points to, because the weld happens at the interface of the two members, not on a side of them. The same is true of backing (a filled semicircle) and surfacing (a gradual ramp): conditions of the joint or surface, not sides of it.

Edge, Scarf and the Remaining Basics

The edge weld symbol looks like two parallel lines and is used on the edges of overlapping sheets in formed sheet metal and diaphragm joints; it carries no location significance. The scarf symbol, a shallow angled line, is the odd one out: it is used for brazed joints rather than welded joints, so it appears on braze drawings, not fusion weld drawings.

Location Significance at a Glance

Symbol group	Basic symbols	Location significance
Groove	Square, V, bevel, U, flare-V, flare-bevel	Arrow side, other side, both sides
Fillet	Fillet	Arrow side, other side, both sides
Plug/slot	Plug, slot	Arrow side, other side, both sides
Resistance/fastener	Spot, seam, projection, stud	None
Condition welds	Back/backing, surfacing, edge	None
Brazing	Scarf	None

Two habits make this library stick. Say each symbol out loud when you see it, “fillet, both sides, five sixteenths,” because speaking forces a full reading instead of a glance. Then sketch them by hand from the chart; drawing a bevel groove ten times beats reading about it. Miller’s guide to reading weld symbols pairs well with the standard, and the National Board’s print reading reference shows the same symbols on boiler and pressure vessel drawings.

Once the glyphs are automatic, the rest of the symbol (sizes, lengths, pitch, flags and tails) becomes reading positions rather than memorized meanings, which is what the next section covers.

Dimensions, Supplementary Symbols and Special Notations

The weld symbol itself only tells you the kind of weld. Everything around it tells you how big it is, how long it runs, how far apart the segments sit, what shape the finished bead should be, and where the welding has to happen. Miss one of those marks and you can cut, fit and weld a joint correctly and still fail inspection.

Reading Dimensions Left and Right of the Reference Line

AWS uses a strict placement rule that never changes: anything left of the weld symbol deals with size or depth, anything right of it deals with length and spacing. The official AWS welding symbol chart lays out every one of these positions.

• Fillet welds: the number on the left is the leg size. If the print specifies throat thickness instead, it appears in parentheses, so “3/8 (1/4)” means a 3/8-inch leg with a 1/4-inch throat.
• Groove welds: the number on the left is the effective size, meaning the depth of fusion into the joint. If the full depth of preparation is different, it is written beside it in parentheses.
• Right of the symbol: a single number is the total length of the weld. Two numbers separated by a dash are length and pitch.

Intermittent Fillets, Staggered Sequences and Number of Welds

On long joints, prints rarely ask for one continuous bead. When the number of welds is specified, the count sits to the left of the symbol, below the size and before the length. A staggered intermittent fillet is marked with a Z-shaped offset between the arrow side and other side symbols, which tells the welder the segments alternate sides rather than line up directly opposite each other.

Groove Angle, Root Opening and Depth of Filling

Preparation geometry gets its own slots. Groove angle goes above the weld symbol, root opening sits inside the symbol, and for plug and slot welds the depth of filling is dimensioned above the symbol with the hole diameter still given as a plug dimension. Miller’s guide to reading weld symbols walks through these placements with shop examples.

Contour Symbols and Finish Designators

Sometimes the shape of the finished weld matters as much as its size. A straight line perpendicular to the reference line placed on the weld symbol means flush or flat; a curved mark means convex or concave. If a specific material removal method is required, a finish letter rides on the contour mark:

Letter	Finish method
C	Chipping
M	Machining
G	Grinding
H	Chipping by hand

This is not cosmetic trivia. In repair and finish-critical work, from alloy wheel repair to aerospace welding, a flush or ground profile is usually the difference between a pass and a reject.

Supplementary Symbols: All-Around, Field Weld, Melt-Through and Consumable Inserts

• Weld-all-around: an open circle at the junction of the arrow and reference line, used on things like pipe-to-baseplate welds that must be continuous around the full perimeter.
• Field weld: a flag at that same junction, meaning the weld is performed on site rather than in the shop. Older drawings may show a filled black circle at the arrow and reference line junction instead of the flag, so watch for it on legacy prints and in field welding inspection guides.
• Melt-through: a solid black crescent on the other side of the reference line, requiring full penetration visible from the back side of the joint.
• Consumable insert: an open crescent on the other side, calling for a preplaced filler metal ring.
• Backing bar: a rectangle above the reference line, or designated in the tail.
• The tail: when present, it carries extra information the symbol can’t hold: the welding process, a code reference, or a detail number. A GMAW process designation in the tail pairs naturally with process references like our aluminum MIG welding guide.

What Changed in the 2020 Edition

The 2020 revision of AWS A2.4 adjusted three symbols you will see called out in ANSI’s coverage of the update:

1. Flash and upset welding symbols were removed. If either process is needed, it is designated in the tail as FW or UW.
2. The diameter symbol is no longer part of the plug weld symbol, though it is still used when dimensioning the plug hole.
3. The flat contour symbol is now limited to fillet welds, while flush is the correct mark for groove, plug and slot welds.

Get these dimensions and supplementary marks right and the weld symbol stops being decoration on a print and starts being a complete fabrication instruction. That full instruction is exactly what you practice reading in the worked examples next.

Reading Real Welding Symbols: Worked Examples from Shop Prints

Knowing the parts of a symbol and reading one under deadline pressure are different skills. The first is theory; the second keeps your grinding wheel off a finished weld. The fastest way to close that gap is to walk through real symbols the way you meet them on a print: one line at a time, in a fixed order, until the habit sticks.

The Repeatable Reading Method

1. Locate the arrow. Find the arrow line and the joint member it touches. That member’s side is the arrow side.
2. Determine the sides. Symbols below the reference line apply to the arrow side; symbols above apply to the other side. Identical symbols above and below mean both sides.
3. Identify the basic symbol. Triangle, V, square, circle, or something else. This tells you the weld type.
4. Read the size on the left. For a fillet, that is the leg. For a groove weld, it is the effective weld size or the groove depth, depending on the notation.
5. Read the length and pitch on the right. Length comes first; a dash and a second number mean pitch, or center-to-center spacing.
6. Check the supplementary marks. All-around circle, field weld flag, contour and finish symbols, melt-through, consumable insert.
7. Read the tail. The tail gives the process, specification, or drawing reference.

That order works regardless of arrow orientation, which is the point. You are not memorizing positions on a page; you are reading relationships between elements.

Example 1: 5/16 Fillet Weld, Both Sides, on a T-Joint

Picture a horizontal reference line with the arrow running down to the vertical leg of a T-joint. A triangle sits below the line, an identical triangle above it, and the number 5/16 sits to the left of the lower triangle. Nothing to the right; the tail is empty.

Read it aloud: a fillet weld on the arrow side and a fillet weld on the other side, both with a 5/16 inch leg. Because the two triangles are identical, the joint gets a continuous fillet on both faces. No length means full length of the joint.

Example 2: Fillet-All-Around with a Field Weld Flag

Now the triangle sits below the reference line with a small circle wrapped around the elbow where the reference line meets the arrow, and the tail end of the reference line carries a small flag.

The circle means weld all around: the fillet continues around the entire perimeter, not just the length the arrow happens to touch. The flag means this is a field weld, made during erection at the job site rather than in the shop. That pennant changes scheduling, access, and inspection: the welder travels to the structure, works in weather, and often welds in a position the shop would never allow. Read it aloud: fillet all around, made in the field. If a size appears on the left, it applies to the whole perimeter.

Example 3: Single-V Groove with Root Opening, Angle, and an Intermittent Fillet

This symbol takes a second longer because it packs in the most common dimension set. The reference line has a V-shaped symbol below it and a triangle above it.

• Below the line: a single-V groove weld on the arrow side. The number to the left of the V is the groove depth or effective weld size. The root opening is written inside the V; the included groove angle sits above or below the V depending on convention.
• Above the line: a fillet on the other side, with its own leg size.
• To the right: a length, then a dash, then a pitch. 3-9 means a 3-inch weld every 9 inches center to center.

That length-and-pitch notation is intermittent welding, and it is where many readers slip. The pitch is not a gap; it is the distance from the start of one weld to the start of the next, per the standard symbol conventions used across welding texts. If the note is followed by the word “staggered,” welds on the opposite side are offset rather than directly opposite, which distributes heat and stress more evenly.

Example 4: Bevel Groove with a Break in the Arrow and a Backing Bar

This one has a detail that catches fitters who skim: the arrow line is not straight. It bends, and the bend lands on one member of the joint. That break tells the reader which member is to be beveled.

The symbol below the reference line is a bevel groove (a half-V). Above the line, a small rectangle marks a backing bar, a strip set behind the joint to support the root pass. A backing bar symbol carries no arrow-side or other-side significance for the weld itself, but its position still tells you where the backing sits. Read it aloud: bevel groove on the arrow side with the arrow-side member prepared, plus a backing bar on the other side. The break in the arrow is the reason the fitter bevels the correct plate instead of cutting the wrong one.

Example 5: Plug Weld with Depth of Filling

A circle on the reference line with a dimension tells a different story. That circle is a plug weld, used when you join two overlapping plates through a hole or slot in the top member. The size to the left is the diameter of the hole or slot.

Inside the symbol, a dimension gives the depth of filling: how much of the hole gets filled with weld metal. When no depth is shown, the hole fills completely. Since the 2020 revision of AWS A2.4, the diameter symbol is no longer required on the plug symbol itself, which cleaned up a long-running confusion. A plug or slot weld has no arrow-side or other-side significance; the circle describes the joint, not a location.

If your shop does aluminum work, plug and slot welds show up often on thin sheet where a full-penetration groove would burn through. The symbol logic is the same, though the practical MIG techniques for aluminum change how the welder actually fills the hole.

Example 6: The Tail with a GMAW Process Note

Finish with the tail. One print might read simply “GMAW”; another might read “GMAW, see detail 4.” Both are instructions layered onto the geometry. The tail closes the loop: arrow side, weld type, size, length, and now the process. If the tail says GMAW and the shop runs a different process by default, you have prevented a procedural error before a torch was lit.

A Verification Habit Worth Building

After reading a symbol aloud using the seven steps, ask two final questions: does the arrow point where I think the prepared member is, and does the tail specify anything that overrides a default? Those two checks catch the majority of real-world rework. Job-site guides echo the discipline, because symbols only work when everyone reads them the same way, which is why the inspection-side checklist mirrors the reading order a welder uses. When print, welder, and inspector follow the same steps, disagreements drop sharply.

Work these six examples a few times and the symbols stop looking like a secret code. They are sentences on a line, and you now know the grammar well enough to read them at the bench.

AWS A2.4 vs ISO 2553 and the Mistakes That Cost Money

A welder trained only on American prints can walk onto a job drawing to international specifications and misread the same glyph twice in a row. The symbol looks familiar, the arrow looks familiar, and that familiarity is what makes it expensive. AWS A2.4 and ISO 2553 share a visual alphabet, but not every rule, and a shop that assumes one system while reading the other will eventually put a bead on the wrong side of a joint.

One Glyph, Two Rulebooks

The structural difference is the reference line. AWS A2.4 uses a single solid reference line, and all side information comes from position: symbols below the line apply to the arrow side, symbols above the line apply to the other side. ISO 2553 adds a dashed identification line running parallel to the solid one, which clarifies the member the arrow is attached to when the arrow alone does not make the prepared member obvious. AWS handles that same situation with a break in the arrow.

Dimensioning is the second divergence. AWS places a fillet size as a plain number, understood as leg length unless stated otherwise. ISO requires a letter with the number: a for design throat or z for leg length. Reading an ISO “a4” as a 4 mm leg oversizes the throat requirement, and reading an AWS 1/4 as a throat undersizes the leg. Units tend to diverge in practice too, with AWS drawings carrying inch fractions such as 5/16 and ISO drawings carrying millimetres.

Element	AWS A2.4	ISO 2553
Reference line	Single solid line	Solid line plus dashed identification line
Side significance	Below = arrow side, above = other side	Similar placement, with the dashed line clarifying the arrow-side member
Fillet dimension	Leg length, no letter	Letter a (throat) or z (leg) required
Prepared member	Break in the arrow	Identification line and arrow convention
All-around and field weld	Circle at junction, flag on the line	Same circle and same flag

The trap is that the same glyph can carry a different placement or a different measurement under each rulebook. A bevel symbol above the line is the other side in AWS, while a drafter working to ISO conventions may have positioned elements relative to the identification line instead. Before you read the size, confirm which standard the drawing declares, usually in the title block, general notes, or a symbol legend.

Seven Mistakes That Cost Money

1. Flipping arrow side and other side. The most expensive error in the trade. Fix it by reading position first: below the reference line is always the side the arrow points to.
2. Ignoring the break in the arrow. The break tells you which member gets the prepared edge. Skip it and you bevel the plate that should have stayed square. Trace the arrow and confirm which member is broken before cutting.
3. Reading pitch as a gap. Pitch is center-to-center spacing of intermittent welds, and the gap is pitch minus weld length. A 3-inch pitch with 2-inch welds leaves a 1-inch gap, not 3 inches.
4. Forgetting the field weld flag. The flag means the weld happens on site, not in the shop, which changes position, procedure, inspection timing, and often the WPS you are allowed to use.
5. Mixing ISO and AWS conventions on one drawing. A frequent cause of wrong-side welds and rework, especially when one sheet in a package came from an overseas engineering firm and the rest from a local detailer. Fix it by declaring a single governing standard in the drawing notes.
6. Missing a staggered intermittent note. Staggered sequences offset the welds on opposite sides of a lap joint. Read only the size and length and you weld chain sequence, distorting the assembly. Check whether the symbols are offset from each other.
7. Assuming arrow direction changes the side rules. The arrow can point up, down, or sideways, but the rules stay anchored to the reference line: below is arrow side, above is other side, no matter how the arrow angles.

These errors show up in every process, from structural carbon steel to aluminum MIG work, because the symbol does not change with the material. The same glyph governs 3/8 plate and thin hull plate alike.

Verification Habits Before the Arc Strikes

• Name the standard first. Look for AWS A2.4 or ISO 2553 in the title block or notes before reading any symbol.
• Read in a fixed order: arrow, sides, symbol, size on the left, length and pitch on the right, supplementary marks, then the tail. Shop-floor reading guides teach the same sequence.
• Speak the weld out loud. “5/16 fillet, arrow side, 2 inches long every 4 inches, all around.” If you cannot say it as one sentence, you have not read it yet.
• Cross-check the weld map and the tail. Process and drawing references in the tail, such as GMAW or a detail callout, confirm you are looking at the right joint.
• Ask before you tack. When a drawing mixes conventions or shows no legend, submit a question to the engineer. Ten minutes of clarification beats a shift of prep, grinding, and rework.

Symbol literacy in both systems keeps a mixed-standard package from turning into a rework budget. Learn AWS A2.4 as your home language, learn enough ISO 2553 to recognize when a drawing is speaking it, and hold the same reading discipline on every sheet that crosses your bench.

How to Learn, Practice and Apply AWS Welding Symbols

Reading a symbol off a page once is easy. Reading it fast, with a fitter waiting and a deadline running, is a different skill, and it only comes from deliberate practice. The good news is that the learning resources are cheap, most of them free, and a few weeks of steady work will take you from deciphering a drawing to speaking its language.

Get the Standard and the Free Chart

Start with the source itself. The current edition, AWS A2.4:2020, Standard Symbols for Welding, Brazing, and Nondestructive Examination, is the document every symbol in this article comes from. Buy it, borrow a copy from your shop’s library, or read the preview pages through ANSI’s published preview to see how the standard is organized before you commit. It reads more like a reference manual than a textbook, so keep it at arm’s length rather than trying to memorize it cover to cover.

Next, print the free AWS Welding Symbol Chart, which AWS publishes for exactly this purpose: shop and classroom use, at no cost. Tape it above your bench, your drafting station, or your laptop. Having the full symbol family, dimension locations, and supplementary marks visible while you work is far more useful than flipping through a PDF twenty times a day.

Draw Symbols by Hand Before You Trust Software

Hand-drawing a dozen symbols does more for retention than reading a hundred. Sketch the reference line, the arrow, the tail, then hang a fillet symbol below it and add a size on the left and a length and pitch on the right. Flip it above the line. Double it. Add the field weld flag. Most print reading courses build their whole first lesson around the same idea, treating the reference line, arrow, and tail as the three main parts of a welding symbol and everything else as detail hung on that frame, as open educational welding courseware does.

Once hand-drawing feels natural, move to CAD. Most fabrication software ships with a welding symbol library, but check which convention it follows: an ISO-style dashed identification line in your library means the tool is drawing ISO 2553 symbols, not AWS ones. Miller’s welding symbol reading guide is a solid free companion for cross-checking what you draw, and state DOT field welding inspection guides, such as New York’s field welding inspection guide, give you real annotated symbols to read against the chart.

Connect Symbols to the Codes That Use Them

Symbols rarely live alone; they sit inside a code. The National Board and ASME-related applications use the same arrow side and other side conventions for pressure equipment drawings, so the rules you learn for a structural print transfer directly to boilers and pressure vessels. In structural work, AWS D1.1 and the related structural welding codes rely on A2.4 symbols to specify weld size, length, and type, which means a misread symbol is a code compliance issue, not just a rework issue.

Formal training accelerates all of this. Print reading classes, AWS certified welder and certified welding inspector preparation, and structured programs such as an aluminium welding course all fold symbol literacy into a broader curriculum, because inspectors and fitters are expected to read symbols as fluently as they read a tape measure.

A Repeatable Practice Routine

Run this cycle for a few weeks and the method becomes automatic:

1. Locate the arrow and name the arrow side and other side before anything else.
2. Identify the basic weld symbol and whether it has location significance.
3. Read size on the left, then length and pitch on the right.
4. Check supplementary marks: all-around circle, field weld flag, contour and finish.
5. Read the tail for process, specification, or drawing references.
6. Write out the symbol in plain English and compare your reading with the chart.

Apply it to real projects, not just exercises. A hull joint from a project like aluminum boat welding, a chassis pass described in aluminum MIG welding, or a repair plan from alloy wheel welding all translate cleanly into symbols you can draw and re-read the next day.

Conclusion: Why Symbol Fluency Advances a Career

The reading method never changes: find the arrow, determine the sides, identify the symbol, read size left and length and pitch right, check the supplementary marks, then read the tail. Run it in that order every single time and you will not put a bead on the wrong side of a joint again.

What separates a welder who reads prints from one who guesses is consistency, and consistency is what employers, inspectors, and certification exams reward. Symbol fluency is one of the few skills that pays off on day one of a job, keeps paying through every code review, and opens the door to fitting, inspection, and engineering-adjacent roles. Learn it properly, practice it deliberately, and every drawing in front of you starts talking instead of whispering.

Frequently Asked Questions

What is an American Welding Society welding symbol?

It is a graphical shorthand defined by AWS A2.4 for specifying welding, brazing, and nondestructive examination requirements on a drawing. A welding symbol always contains a horizontal reference line and an arrow, and may add a weld symbol, dimensions, supplementary symbols, and a tail for process or specification notes.

What is the difference between a weld symbol and a welding symbol?

A weld symbol is the small glyph that indicates the type of weld, such as a triangle for a fillet weld. A welding symbol is the complete assembly — reference line, arrow, weld symbol, dimensions, supplementary symbols, and tail — that describes how the weld is to be made.

How do I know whether the weld goes on the arrow side or the other side?

Anything written below the reference line applies to the arrow side, the side the arrow points at. Anything above the line applies to the other side, the opposite side of the joint, and this rule holds no matter which direction the arrow points.

What does the flag on a welding symbol mean?

A flag at the junction of the arrow and reference line is the field weld symbol, meaning the weld is made on site during erection rather than in the shop. Older drawings sometimes used a filled black circle at that junction to mean the same thing.

What does the circle at the arrow junction mean?

An open circle at the arrow/reference line junction is the weld-all-around symbol, which means the weld extends completely around the joint, such as a fillet weld around a pipe or a full perimeter of a bracket.

What do the two numbers after a fillet weld symbol mean?

The first number is the fillet weld size, placed to the left of the symbol. The second pair describes intermittent welds: the length of each segment and the pitch, which is the center-to-center spacing between segments.

What is in the tail of a welding symbol?

The tail carries supplementary information such as the welding process (for example SMAW, GMAW or FCAW), a specification, a procedure number, or a detail reference. If no such reference is needed, the tail is simply omitted.

How does AWS A2.4 differ from ISO 2553?

ISO 2553 uses a solid reference line plus a dashed identification line to distinguish sides, and requires letters such as ‘a’ for throat or ‘z’ for leg on fillet dimensions. AWS A2.4 uses a single reference line with position above or below conveying the side, and dimensions fillet size by leg length without a letter.