Sources and scope for this page: AWS A2.4:2020, covering every symbol, category and reference-line convention on this page. No independent source check is recorded for this page: the content rests on the sources listed and on the working shown on the page. Full sources, values and limits on this page.
Page last changed 2026-11-08 · based on AWS A2.4:2020
Quick Answer
A welding symbol has three parts that matter most: the arrow points to the joint, the reference line carries the symbol, and position above or below the line decides which side the weld is made on. A symbol above the line means the arrow side; below means the other side.
AWS A2.4 Welding Symbols
| Symbol[1] | Name[1] | Category[1] | What it means[1] |
|---|---|---|---|
| △ # | Fillet weld | Arc / groove | The most common weld. A triangular symbol on the reference line, with the vertical leg on the left. Leg size goes to the left of the symbol, length to the right. |
| ▯ # | Square butt weld | Groove | Two parallel plates butted together with no edge preparation. Only suitable for thin material — typically up to about 3/16 in. |
| V # | V-groove weld | Groove | Both plates bevelled to form a V. The standard groove for full-penetration joints in plate from about 1/4 in upward. |
| Ⅴ # | Bevel groove weld | Groove | One plate bevelled, the other square — a half-V. Used where access from one side only is practical. |
| U # | U-groove weld | Groove | Both plates prepared with a curved (J-shaped in section) edge. Needs more preparation than a V but uses less filler metal on thick sections. |
| J # | J-groove weld | Groove | One plate curved, the other square — the single-bevel analogue of a U-groove. |
| ⌄ # | Flare-V groove weld | Groove | For joining two curved surfaces, such as tube to plate. The V is formed by the natural curvature, not by machining. |
| ⌐ # | Flare-bevel groove weld | Groove | The single-curved-surface analogue of the flare-V, used where only one member is curved. |
| ⌾ # | Plug weld | Arc | A hole in one member filled with weld to fuse it to the member beneath. Often used for lap joints and for slot-and-tab assemblies. |
| ▭ # | Slot weld | Arc | Similar to a plug weld but the hole is elongated. Strength is proportional to the filled area of the slot. |
| ⊙ # | Spot weld | Resistance | A resistance weld made at a point. Shown without a size dimension on the symbol; the number of spots is given in the tail or by convention. |
| ≡ # | Seam weld | Resistance | A continuous resistance weld made by overlapping spots. Size is shown as the width of the weld, not its length. |
| ⌐⌐ # | Back weld | Supplementary | A weld made on the reverse side after the first pass has been completed, usually to ensure full penetration. Applied after the primary weld. |
| ⌐ # | Backing weld | Supplementary | A weld made on the reverse side before the primary weld, providing a backing for the root pass. Applied before, unlike a back weld. |
| ⌴⌴ # | Melt-through | Supplementary | Indicates that the weld must be visible on the reverse side as a result of full penetration, without an additional pass. |
| ◠ # | Surfacing weld | Supplementary | A weld deposited to build up a surface rather than to join — hardfacing, corrosion-resistant overlay and similar. |
| ▱ # | Edge weld | Arc | A weld along the edge of a member, used mainly on sheet metal and where the members overlap at an edge. |
| ⌐ # | Corner weld | Arc | A weld joining two members at right angles by fusing one or both edges — distinct from a fillet, which fills a corner. |
| ⌒ # | All-around | Supplementary | A circle at the junction of the reference line and the arrow. Means the weld is applied around the entire joint, not just where the arrow points. |
| ▲ # | Field weld | Supplementary | A solid flag at the same junction. Means the weld is made at the site rather than in the shop, and the applicable field procedure governs. |
| ⟟ # | Tail | Supplementary | The tail of the reference line carries the process, specification or procedure reference — for example GTAW or a procedure number. A tail omitted means the process is not specified. |
| ⌒ # | Flush contour | Supplementary | A straight line added to the weld symbol. The finished weld must be flush with the surface — no reinforcement. |
| ⌢ # | Convex contour | Supplementary | A curved line above the symbol. The finished weld must be convex — reinforcement is required. |
| ⌣ # | Concave contour | Supplementary | A curved line below the symbol. The finished weld must be concave — the reinforcement must be removed. |
| ⟂ # | Backing / spacer | Supplementary | A rectangle on the reference line. Either indicates a backing strip is used, or — with a letter in it — identifies a specific backing material. |
| ① # | Contour and finish | Supplementary | A contour symbol together with a finish method letter and grade symbol in the tail, controlling the as-welded surface. |
| — # | Solid reference line | Reference line | The main line the weld symbol sits on. A symbol above the line means the weld is made on the arrow side; below the line means the other side. |
| — # | Dashed reference line | Reference line | Appears below the solid line when both sides of the joint are welded. A symbol on the dashed line means the weld goes on the other side. |
| — # | Arrow | Reference line | Points to the joint. For a fillet weld the arrow points to the member that the weld is applied to, which determines which leg is dimensioned. |
| — # | Arrow side | Reference line | The side the arrow touches. Symbols above the reference line apply here. |
| — # | Other side | Reference line | The opposite side. Symbols below the reference line apply here. |
Symbols are grouped by category: groove and arc welds form the joint, supplementary symbols modify how the weld is made or finished, and the reference-line conventions govern placement. Dimensioning rules (leg size, length, pitch) are not reproduced here.
Reading the Reference Line
Most misread welding symbols are not misread at the symbol — they are misread at the line. The rules:
- The arrow points to the joint and defines two sides. The side the arrow touches is the arrow side; the side away from it is the other side.
- A symbol placed above the reference line applies to the arrow side.
- A symbol placed below the reference line applies to the other side.
- When both sides are welded, the reference line becomes a pair: a solid line with a dashed line beneath it. Symbols on the solid line are arrow-side, on the dashed line other-side.
- The tail, where present, names the process or the procedure to be used. No tail means the process is not specified on the drawing.
For a fillet weld specifically, which member the arrow points to matters: it determines which leg is the size dimension and which is the length.
Groove Welds and Joint Preparation
Groove welds are used for full-penetration joints and require edge preparation. The choice between them is driven by thickness, access and cost:
- Square — no preparation, but only practical on thin material. Cheapest per metre of weld until penetration stops being achievable.
- V and bevel — the workhorses. A V gives access from both sides; a bevel where only one side is accessible. Required weld volume rises sharply with thickness because the groove is triangular in section.
- U and J — curved preparation, more expensive to machine but a narrower groove, so much less filler metal on thick sections. On heavy plate the machining pays for itself.
- Flare-V and flare-bevel — for curved members where the groove is formed by the existing curvature, so no preparation is needed at all.
Frequently Asked Questions
- What does a triangle symbol mean in welding?
- A fillet weld — the most common weld type. The triangle sits on the reference line and the vertical leg is drawn on the left. Leg size is dimensioned to the left of the symbol and length to the right.
- What is the difference between a welding symbol and a weld symbol?
- The weld symbol is the part that identifies the weld type — the triangle for a fillet, the V for a V-groove. The welding symbol is the whole assembly: reference line, arrow, tail and any supplementary symbols. The distinction matters when reading a drawing because dimensions attach to specific parts of the assembly.
- What does a flag on a welding symbol mean?
- A field weld — the weld is to be made at the installation site rather than in the shop. It is drawn as a solid flag at the junction of the arrow and reference line, and it means the applicable field welding procedure governs.
- What does a circle at the corner of a welding symbol mean?
- An all-around weld. The weld is applied around the entire joint, not only where the arrow points. It is drawn as a circle at the junction of the arrow and the reference line.
- What does the tail of a welding symbol contain?
- The welding process, specification or procedure reference — for example the process abbreviation such as GTAW or SMAW, or a procedure number. When the tail is omitted, the welding process is not specified on the drawing and is left to the fabricator's procedure.
- What does a symbol below the reference line mean?
- The weld is made on the other side — the side away from the arrow. Symbols above the line apply to the arrow side. Where both sides are welded, a dashed line is added beneath the solid reference line and the lower symbols apply to the other side.
Related
Value Sources
References and calculation methods used for this page are listed below. Numbered markers connect table columns where present. A reference listing does not itself establish that every value has been independently checked.
| # | Source | Type | Revision / method |
|---|---|---|---|
| [1] | AWS A2.4 — Standard Symbols for Welding, Brazing, and Nondestructive Examination | reference | AWS A2.4:2020 — source |
Data Sources
| Standard | Revision | What it covers on this page |
|---|---|---|
| AWS A2.4 — Standard Symbols for Welding, Brazing, and Nondestructive Examination | AWS A2.4:2020 | every symbol, category and reference-line convention on this page |
Verification scope
No page-specific independent source review is recorded here. The listed references and formulas explain the basis of the compilation; automated consistency checks do not verify the original sources or establish product conformity.
This page explains what each symbol means. It does not cover the dimensioning rules — leg size, length, pitch, groove angle and root opening — which are all part of the standard and are what a welder actually works from. Obtain the standard for production drawing work.
Accuracy and use. Use the source notes and recorded verification scope above to assess each value. Calculated values follow the stated derivations; compilation values may lack a confirmed original document or product condition. No warranty, express or implied, is made as to the accuracy or completeness of this information, and no liability is accepted for any loss or damage arising from its use. Engineering reference data is provided for guidance in preliminary work — before a value is used for design, fabrication or acceptance testing, verify it against the current revision of the governing standard and against your own inspection. The user assumes all risk and responsibility in connection with the use of this information.
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