Weld Symbol Reference (AWS A2.4)
Complete weld symbol guide per AWS A2.4 — fillet, groove (V, bevel, U, J, square, flare), plug, slot, spot, seam, surfacing, and back/backing welds. Position, side conventions, all-around, field, and contour symbols.
Reference
Weld symbols on a drawing tell you exactly where, how big, and what type of weld to lay down — without ambiguity. The reference line + arrow points at the joint; symbols below the line apply to the arrow side (the side the arrow points to); symbols above the line apply to the other side of the joint. The tail (right end) carries notes / specifications. This page covers AWS A2.4 (US) — ISO 2553 differs in some conventions.
Symbol layout — anatomy of the line
Other side (e.g. fillet)
┌───┐
│ │
────────┴───┴────────── ← reference line
╲ ┌───┐
╲ │ │
╲ └───┘ (e.g. fillet on arrow side)
╲ Arrow side
─────────╲
─────► arrow (points to joint)
Tail at right end of reference line → process / notes / specification:
────/───SMAW(7018)───tail ← process and reference
Above the reference line = "other side" (the side opposite where the arrow lands).
Below the line = "arrow side".
Symbols on both above and below = weld both sides.
Numbers before the symbol = leg / depth size (e.g. 1/4 for 1/4" fillet leg). Numbers after the symbol (in parentheses) = root opening / groove angle.
Numbers far right separated by dashes = length × pitch for intermittent welds (e.g. 2-6 = 2" weld every 6" spacing).
Weld type symbols (AWS A2.4)
| Symbol | Weld type | When to use |
|---|---|---|
| ▷ | Fillet | T-joint, lap joint, corner joint at 90°. Most common weld in fabrication. |
| ▽ | V-groove | Butt joint, both edges beveled. Good penetration on plate > 3/16". |
| ▽▽ | Double V-groove | Plate > 3/4". Welded both sides; reduces distortion. |
| ∠ | Bevel-groove | One side beveled, other square. Good for T-joints needing penetration. |
| ∪ | U-groove | Heavy plate; less filler than V-groove for same depth. |
| ∫ | J-groove | One side U-shaped, other square. Like bevel but less filler. |
| ∥ | Square groove | Butt joint, no edge prep. Plate ≤ 3/16" only. |
| ⌣⌣ | Flare-V groove | Two rounded edges (e.g. tube to tube). |
| ⌒ | Flare-bevel | One rounded edge to flat (tube to plate). |
| ⊙ | Plug / slot | Filling a pre-drilled hole (or slot) in the upper plate to weld it to the lower. |
| ○ | Spot | Resistance spot weld (RSW); thin sheet stack-up. |
| ═ | Seam | Continuous resistance seam weld (sheet metal). |
| ⌒ | Back / backing | Weld on opposite side AFTER initial weld is finished. Different from a simple "other side" weld. |
| ⌒⌒ | Surfacing | Build-up of material onto a surface; not a joint. Show as crescents. |
| ▷ ▷ ▷ | Stud | Stud welding (CD or arc-stud). |
Supplementary symbols
| Symbol | Meaning | Where placed |
|---|---|---|
| ○ on arrow / line junction | Weld all-around | Circle at the elbow of the arrow / reference line. Walk the joint completely. |
| ▼ (filled flag) | Field weld | Black flag at the elbow. Means "weld at the job site, not in the shop." |
| — (flat dash above weld) | Flush / flat contour | Bead must be ground / machined flush. |
| ⌒ (curved cap) | Convex contour | Bead allowed to be raised above surface naturally. |
| ⌣ (curved well) | Concave contour | Bead must be ground concave (typical for fatigue-critical). |
| M / G / C / R finish letter | Finish method | Letter goes after the contour symbol. M=machined, G=ground, C=chipped, R=rolled. |
| Tail with reference to spec | Procedure / process / spec | Tail at right end. e.g. SMAW E7018-1 or per WPS-23. |
| Letter / number in tail | Welder qualification / no spec | NO SPEC means no notes. Or qualification level (3G, 6G). |
Reading examples
1/4 ▷
1/4-inch fillet weld on the arrow side only.
▷ 1/4 ────── 1/4 ▷
1/4-inch fillet on BOTH sides (above AND below the line).
3/16 ▷ 2-6
3/16-inch intermittent fillet — 2-inch weld bead every 6 inches center-to-center.
5/16 ▽ 60° (1/8)
5/16-inch deep V-groove, 60° included angle, 1/8-inch root opening.
▷ ⊕ ▼
Fillet weld, all-around, field weld (job-site).
3/8 ▷ G
3/8-inch fillet, ground flush. The "G" is the finish-method letter under the flat-contour symbol.
Fillet weld dimensions
| Spec | Position on symbol | Meaning |
|---|---|---|
| Leg size | Number to LEFT of fillet symbol | 1/4 = 1/4" leg (the equal-leg dimension on each plate). |
| Throat (rare) | Letter "T" + number, or in tail | Specifies effective throat instead of leg. |
| Length | Number to RIGHT of fillet symbol | 1/4 ▷ 6 = 1/4" fillet, 6" long. |
| Pitch (intermittent) | After length, separated by dash | 1/4 ▷ 2-6 = 2" weld, repeat every 6". |
| Both legs different | Two numbers with × between | 1/4 × 3/8 ▷ = unequal-leg fillet, 1/4 vertical × 3/8 horizontal. |
| Number of welds | Number with × at end | 1/4 ▷ 3 × 4 = three 4" welds. |
Groove weld dimensions
| Spec | Position on symbol | Meaning |
|---|---|---|
| Depth of preparation | Number to LEFT of groove symbol | How deep the bevel is cut. |
| Effective throat | Number in PARENTHESES to LEFT | Effective weld throat after CJP / PJP. |
| Groove angle | Number BELOW the symbol | 60° = 60-degree included groove angle. |
| Root opening | Number BETWEEN the lines, in parens | (1/8) = 1/8" gap at root. |
| Single bevel side | Arrow point with break | Arrow break shows which plate is beveled (not the arrow direction). |
| CJP (full penetration) | No depth specified | Complete-joint penetration weld; weld through full thickness. |
AWS A2.4 vs ISO 2553 — major differences
- Reference line
- AWS uses single line; ISO 2553 uses dual line (one solid, one dashed). The dashed line indicates the "other side" — symbols are placed by which line they are below.
- Arrow side
- AWS: below = arrow side. ISO 2553: depends on which line the symbol is below (more explicit).
- Throat / leg
- AWS uses leg by default; ISO 2553 uses throat (often denoted "a" prefix). Convert: throat = leg × 0.707 for equal-leg fillet.
- Process
- AWS: 4-letter abbreviation in tail (SMAW, GMAW). ISO: numeric process code (111=SMAW, 135=GMAW).
- When in doubt
- Check the title block of the drawing — it should call out the standard (AWS A2.4 or ISO 2553).
Process codes (tail abbreviations — AWS)
- SMAW
- Shielded Metal Arc Welding (stick).
- GMAW
- Gas Metal Arc Welding (MIG / MAG).
- GMAW-S
- GMAW short-circuit transfer.
- GTAW
- Gas Tungsten Arc Welding (TIG).
- FCAW
- Flux-Cored Arc Welding.
- FCAW-S
- FCAW self-shielded (gasless).
- SAW
- Submerged Arc Welding (granular flux).
- PAW
- Plasma Arc Welding.
- OAW / OFW
- Oxy-acetylene gas welding.
- RSW
- Resistance Spot Welding.
- RSEW
- Resistance Seam Welding.
- EBW
- Electron Beam Welding.
- LBW
- Laser Beam Welding.
- FW
- Flash Welding (resistance, end-to-end).
Common drafting mistakes
- Symbol on wrong side of line: above = other side, below = arrow side. Reversing them puts the weld on the wrong side of the joint.
- Missing leg size: a fillet symbol with no number is ambiguous. AWS-defaults vary by code (D1.1 says minimum per material thickness), but always specify.
- "Weld both sides" written in tail: not standard. Put symbols above AND below the reference line instead.
- All-around circle on flat single-line joint: only valid where the joint actually goes around something (closed loop). Pointing at a single straight seam, the all-around circle is meaningless.
- Field-weld flag pointing inward: per AWS, the flag tip points away from the reference line. Some older drawings have it pointing toward the line — both are usually understood but A2.4 is specific.
- Confusing back-weld with double-V: a back-weld symbol is a small ⌒ opposite the main groove symbol. A double-V is two ▽ stacked. Different welds.
Notes
- Symbols rendered here are simplified ASCII / Unicode approximations — refer to AWS A2.4 standard or any drafting handbook (Machinery's Handbook chapter 30) for the precise scaled symbols used on production drawings.
- For ISO 2553 work and dimensional tolerancing, see ISO 2553 directly. Many shops in mixed-spec environments simply write "AWS" or "ISO" in the title block to indicate which standard governs.
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