Welding Symbols: ISO 2553 vs AWS A2.4
All 22 weld symbols compared across ISO 2553 System A/B and AWS A2.4, with arrow-side rules, a/z throat conversions and intermittent-weld counting examples.
Weld symbols compared: ISO 2553 (2019) vs AWS A2.4 (2020), 22 types
| No. | Weld type | Symbol form (text description) | ISO 2553 (A / B) | AWS A2.4 | Arrow side / other side | Dimension notation (ISO → AWS) | Typical application | Common misreading | Source |
|---|---|---|---|---|---|---|---|---|---|
| 1 | Fillet weld | right triangle, legs on the reference line, hypotenuse outward | Table 1 No.10; clause 5.5 — A: solid line = arrow side, dashed = other side; B: below = arrow side | §8; triangle; bare number on the left | A vs B/AWS directions are opposite; mirrored when welded both sides | ISO a (throat) or z (leg) left, length right → AWS bare number = leg left, length-pitch right | T, lap and corner joints — the everyday weld | reading a as a leg, or reading up/down in System A | S1, S5, S6, S8 |
| 2 | Square / I butt weld | two short parallel vertical lines, no preparation | Table 1 No.1; clause 5.4 | §7 square groove; two parallel lines | groove rules; one symbol for single-side welds | ISO s = penetration; no size = full penetration → AWS D(S) + R (root opening) | thin sheet, low current, single side | assuming no size means anything goes — ISO defaults to full penetration | S1, S11, S6 |
| 3 | Single-V groove | symmetrical V opening, apex on the line | Table 1 No.2; clause 5.4 | §7 V-groove | single-side preparation on one member; double side = X | ISO s penetration, α on the symbol → AWS D(S), R, α | medium plate, single-side full penetration | reading s as preparation depth, or the root gap as penetration | S1, S6, S7 |
| 4 | V with root face (Y) | V with a short flat land at the bottom — reads like a Y | Table 1 No.3; clause 5.4 | no separate symbol — V plus root-face note | same as V | ISO s + root face depth (letter: declared gap) → AWS D(S) + note | burn-through control, thick plate, single side | treating it as a plain V and losing the root face | S1, S11, S6 |
| 5 | Double-V (X) | two V shapes sharing the root, forming an X | Table 2 combination No.1; symmetric double-sided may omit the dashed line | §7 double-V | symmetric — no arrow/other-side meaning | ISO s per side (no total) → AWS D(S) per side + α | thick plate, both sides accessible, distortion control | adding the two sides' penetrations into a total | S1, S11, S6 |
| 6 | Single-bevel groove | half a V: one vertical edge + one inclined edge | Table 1 No.4; clause 5.3 — arrow points at the prepared member | §7 bevel; §6.4 broken arrow points at the prepared member | ISO arrow marks the prepared plate; AWS uses the broken arrow | ISO s + bevel angle β → AWS D(S), R, α | T-joints, preparation possible on one member only | arrow on the wrong plate — the bevel ends up on the unprepared one | S1, S2, S6 |
| 7 | Double-bevel (K) | two half-Vs back to back, forming a K | Table 2 combination No.2; symmetric | §7 double-bevel | symmetric, no side meaning | one set per side | thick T-joints, both sides accessible | confusing K with X; reading the bevel directions backwards | S1, S11, S6 |
| 8 | Single-U groove | U shape: rounded bottom + two vertical sides, usually with a root face | Table 1 No.6; clause 5.4 | §7 U-groove | same as V | ISO s, R (root radius), root face → AWS D(S), R, α | thick plate, narrow preparation, filler savings | confusing with J (J has one rounded side only) | S1, S6, S13 |
| 9 | Double-U | two U shapes stacked | Table 2 combination No.5; symmetric | §7 double-U | symmetric, no side meaning | one set per side | very thick plate | treating as double-V; losing the root radii | S1, S11, S6 |
| 10 | Single-J groove | half a U: one vertical side + one rounded side | Table 1 No.7; clause 5.3 — arrow points at the prepared member | §7 J-groove; broken arrow | ISO arrow marks the prepared side; AWS broken arrow | ISO s, R, root face → AWS D(S), R | thick plate single-side, nozzles and tubes | confusing with single-U; arrow on the wrong side | S1, S2, S6 |
| 11 | Double-J | two J shapes stacked | Table 2 combination (J both directions); symmetric | §7 double-J | symmetric, no side meaning | one set per side | very thick plate, both sides accessible | direction read backwards | S1, S11, S6 |
| 12 | Flare-V groove | two outward-flaring arcs forming a wide-mouth V | Table 1 No.8 | §7 flare-V | groove rules; arrow at the joint | ISO s → AWS effective throat from the radius via the D1.1 prequalified table (coefficient varies by edition) | tube or rounded profile butt-welded to plate | using the 0.707 fillet factor — overstates the throat | S1, S6, S15 |
| 13 | Flare-bevel groove | one flaring arc + one straight edge — half a flare mouth | Table 1 No.9 | §7 flare-bevel | bevel rules; arrow at the joint | ISO s → AWS coefficient from R and process, see the flare-bevel question (§ Q13) | tube onto plate, rounded-to-flat joints | computing the throat with plain-bevel geometry | S1, S6, S15 |
| 14 | Plug weld (round hole) | rectangle representing the hole, filled with weld | Table 1 No.11; clause 5.6 | §9 plug weld; rectangle | arrow points at the drilled member | ISO d hole dia left, fill depth inside (omit = fill flush) → AWS dia (Ø still used for the size), depth inside, pitch right, count in brackets | lap joints, one side accessible, closed structures | reading the hole diameter as a leg size | S1, S11, S7 |
| 15 | Slot weld | elongated rectangle, filled with weld | Table 1 No.11; clause 5.7 | §10 slot weld; rectangle | arrow points at the slotted member | ISO width c left, fill depth inside → AWS width + length left, depth inside, pitch right, count in brackets | long slots, reinforcement connections | swapping slot width and length | S1, S11, S7 |
| 16 | Spot weld (resistance or arc) | hollow circle centred on the reference line | Table 1 No.12 (resistance) / No.13 (arc); clause 5.8 | §11 spot weld; hollow circle | symmetric — no arrow/other-side meaning | ISO d nugget dia left, n × (e) right → AWS size left (2020: size only, no strength), pitch right, count in brackets | thin sheet laps: automotive, appliances | reading d as a leg; reading e as a centre distance | S1, S11, S6, S12 |
| 17 | Seam weld (resistance or arc) | ISO: rectangle with a centre line; AWS: circle with two parallel lines | Table 1 No.14 / No.15; clause 5.9 | §12 seam weld | no side meaning | ISO width c left; intermittent n × l (e) right → AWS size left, length-pitch right | sealed seams: tanks, ducting, tubes | continuous vs intermittent swapped; width read as depth | S1, S11, S6, S15 |
| 18 | Stud weld | ISO: dedicated stud symbol (official graphic unverified — declared gap); AWS: circle with an X | Table 1 No.16; clause 5.11 | §14 stud weld; circle-X | arrow side only — no other-side usage | ISO d stud dia left, n × (e) right → AWS size left, pitch right, count below in brackets | shear studs: construction, bridges, façades | treating as a spot weld; dropping count/pitch | S1, S11, S6, S15 |
| 19 | Edge weld | ISO: three short parallel vertical lines; AWS: three short legs under a cap | Table 1 No.19; clause 5.10 | §13 edge weld — different shape from the ISO form | one side; arrow at the edge | ISO plate thickness left → AWS size/thickness note | thin sheet edges: flanges, closed borders | confusing with flanged welds; cross-reading the two shapes | S1, S11, S13, S6, S15 |
| 20 | Flanged butt / corner weld | two outward-flaring lines (an open eight), edge fully melted | Table 1 No.20 | §13 edge weld covers flanged butt/corner | one side; arrow at the flange | ISO plate/flange size → AWS size note | thin sheet: appliances, vessels, ducting | treating as a V preparation; missing the full-fusion requirement | S1, S13, S6 |
| 21 | Surfacing / build-up | wavy line along the reference line | Table 1 No.21; clause 5.12 | §15 surfacing; wavy line | no side meaning | ISO layer size per clause 5.12 → AWS size left | wear layers, repair, cladding | mistaking for a seam weld | S1, S11, S6, S15 |
| 22 | Backing run / back weld (and backing strips) | open half-circle supplementary symbol on the far side; distinguish from backing-strip symbols; AWS melt-through is a filled half-circle | Table 3 No.5 (backing run); No.7a–7c (backing strips) | §7.7 backing / back weld | far-side half-circle = weld-from-the-back; multiple reference lines sequence the operations | no size; process/sequence in the tail or on additional reference lines | single-side full-penetration joints with a sealed root | confusing the backing strip (a part) with the backing run (a weld) | S1, S11, S6, S15 |
How to read this table. Identify the system before reading any symbol: a solid reference line plus a dashed identification line is ISO System A (line type alone decides the side, never up/down); a single reference line is ISO System B or AWS, where below the line = arrow side and above = other side. A and B must never be mixed on one drawing, and the drawing must state the system. ISO sizes fillets with a (throat) or z (leg); AWS uses a bare number = leg size. Undimensioned ISO butt welds default to full penetration; AWS requires CJP to be stated. Symbol shapes here are text descriptions — the ISO stud-weld graphic and the root-face letter remain declared gaps.
In AWS A2.4, is a weld symbol above the reference line on the arrow side or the other side?
Other side. Below = arrow side, above = other side — two positions, one rule (§6.1). Never import ISO System A's solid/dashed logic onto an AWS drawing:
| System | Reference line | Arrow side | Other side | Symmetric double-sided |
|---|---|---|---|---|
| ISO 2553 System A | solid line + dashed identification line (dashed may be above or below) | symbol on the SOLID line (either up or down) | symbol on the DASHED line | one symbol each; symmetric pairs may omit the dashed line |
| ISO 2553 System B | single solid line | symbol BELOW the line | symbol ABOVE the line | one symbol each side |
| AWS A2.4 | single solid line (always horizontal) | symbol BELOW the line (§6.1) | symbol ABOVE the line (§6.1) | one symbol each; staggered by offsetting, no Z mark |
How much throat thickness is lost if an ISO a6 fillet is fabricated as a 6 mm leg?
The throat drops from 6.00 to 4.24 mm (−29.3%); the area drops from 36 to 18 mm² — exactly half, because area scales with the square. One letter is one weld-length of filler:
| Step | Item | Basis | Value |
|---|---|---|---|
| 1 | Leg required for a6 | z = a × √2 | 6 × 1.4142 = 8.485 mm |
| 2 | Throat actually built at z6 | a = z / √2 | 6 / 1.4142 = 4.243 mm (−29.3%) |
| 3 | Section area required / actual | A = a² / A = z²/2 | 36.0 vs 18.0 mm² (−50%) |
| 4 | Metal over 8 m of weld | V = A × 8,000 mm | 288 vs 144 cm³ — a 144 cm³ shortfall |
| 5 | Moral | — | z = a√2, A = z²/2, V = A×L — three lines catch the whole error |
What leg length satisfies an ISO a5 throat?
z = 5 × 1.414 = 7.07 mm; a z7 gives 4.95 mm (1% under), z8 gives 5.66 mm (13% over). Conversions you will actually use:
| Drawing callout | Converts to | Note |
|---|---|---|
| a4 | z ≈ 5.7 mm | z = a × 1.414 |
| a5 | z ≈ 7.07 mm | z7 = 4.95 mm throat (1% under); z8 = 5.66 mm (13% over) |
| a6 | z ≈ 8.49 mm | the worked example above |
| z6 | a ≈ 4.24 mm | a = z / 1.414 |
| z8 | a ≈ 5.66 mm | if the buyer wants an 8 mm throat they must write a8 (leg ≈ 11.3 mm) |
| AWS bare 6 | leg = 6 mm, throat ≈ 4.24 mm | AWS numbers are legs already — do not divide again |
What does AWS 12(10) mean on a groove weld?
Groove depth D = 12 mm, weld size / effective throat (S) = 10 mm — 83.3% of the depth. Pre-2012 drawings may write S(E) instead; read them by their own edition:
| AWS edition | Notation | Meaning |
|---|---|---|
| A2.4:2012 and later (incl. 2020) | D(S) — D = groove depth, (S) = weld size / effective throat | 12(10) = 12 mm deep, 10 mm effective throat |
| Before A2.4:2012 | S(E) — S = depth placeholder, (E) = effective throat | same physical meaning, different letters — do not read an old drawing with the new rules |
How many weld elements does AWS 75-150 produce on a 6000 mm beam?
40 elements per side: floor((6000 − 75) / 150) + 1 = 40, total 3000 mm of weld per side — 50% of the member. Double-sided that is 108 cm³ of fillet metal at z6.
| Step | Item | Value |
|---|---|---|
| 1 | Count (pitch = centre-to-centre) | n = floor((6000 − 75) / 150) + 1 = 40 per side |
| 2 | Weld length per side | 40 × 75 = 3000 mm |
| 3 | Fillet metal | A = z²/2 = 18.0 mm²; 3000 × 18.0 = 54.0 cm³ per side; 108.0 cm³ both sides |
| 4 | ISO equivalent notation | e = 150 − 75 = 75 → n × l (e) = 40 × 75 (75) |
If 150 is misread as ISO edge-to-edge e, how many elements result?
27 elements per side instead of 40: unit period becomes 75 + 150 = 225 mm, so the beam carries 2025 mm of weld — 975 mm (−32.5%) short. The whole error is one word: pitch versus gap.
| Item | ISO n × l (e) | AWS length-pitch |
|---|---|---|
| Position | right of the symbol | right of the symbol |
| Count | n written explicitly | count in brackets / inferred |
| Length | l = length of each element | length left of the hyphen |
| Spacing meaning | (e) = clear gap, edge to edge | pitch = centre to centre |
| Conversion | pitch = l + e; e = pitch − l | same relation, other side of the equation |
| Staggered elements | Z mark on the reference line | offset symbols above/below, no Z |
| The 75-150 case | misread as e: period 225 mm → 27 elements, 2025 mm (−32.5%) | pitch 150 → 40 elements, 3000 mm |
What is the minimum AWS D1.1 fillet leg for 10 mm plate?
3/16 in = 5 mm (T over 6 mm up to 12 mm). The table below sets the size the symbol must carry; 3/16 in is the rounded 4.76 mm and the source is a secondary digest — verify against the purchased D1.1 edition:
| Base metal thickness T | Minimum leg (in) | Minimum leg (mm) | Note |
|---|---|---|---|
| T ≤ 1/4 in (≤ 6 mm) | 1/8 in | 3 mm | cyclically loaded structures take 3/16 in (5 mm) |
| 1/4 in < T ≤ 1/2 in (6–12 mm) | 3/16 in | 5 mm | rounded value; D1.1 tabulates inches (4.76 mm exact) |
| 1/2 in < T ≤ 3/4 in (12–20 mm) | 1/4 in | 6 mm | — |
| T > 3/4 in (> 20 mm) | 5/16 in | 8 mm | — |
What is the minimum AWS D1.1 fillet leg for 25 mm plate?
5/16 in = 8 mm (T over 20 mm). Which member T refers to varies with process and preheat — low-hydrogen processes usually take the thinner member; settle T against the D1.1 text, this table only carries the values.
| Base metal thickness T | Minimum leg (in) | Minimum leg (mm) |
|---|---|---|
| T > 3/4 in (> 20 mm) — covers 25 mm plate | 5/16 in | 8 mm |
| 1/2 in < T ≤ 3/4 in (12–20 mm) | 1/4 in | 6 mm |
How wide is a 60° V groove at 12 mm depth with a 2 mm root gap?
Top width 15.86 mm; groove area 107.1 mm², i.e. 107.1 cm³ of filler per metre — plain geometry with the inputs declared, ignoring root face and cap.
| Step | Item | Value |
|---|---|---|
| 1 | Inputs (declared) | angle 60°, depth 12 mm, root gap 2 mm |
| 2 | Top width | 2 × 12 × tan 30° + 2 = 13.86 + 2 = 15.86 mm |
| 3 | Cross-section area (trapezoid) | 12 × (15.86 + 2) / 2 = 107.1 mm² |
| 4 | Filler per metre | 107.1 mm² × 1000 mm = 107.1 cm³/m |
Does an undimensioned ISO butt weld mean partial penetration?
No — zero dimensions = full penetration by default (Table 1 footnote b). AWS does not default from blank space: CJP must be stated:
| System | Default reading | Source |
|---|---|---|
| ISO 2553 | no size on a butt weld and no other note → full penetration assumed | S1, S11 |
| AWS A2.4 | no blank-space defaults — CJP by note/symbol, PJP by D(S) | S7 |
Can ISO System A and System B be mixed on one drawing?
No — one system per drawing; the drawing must state system and units (0 mixing allowed). Judge an unfamiliar drawing in this order:
| Step | Evidence on the drawing | Verdict | Risk if ignored |
|---|---|---|---|
| 1 | solid reference line AND a parallel dashed line, symbols on both | ISO System A — line type decides the side, never up/down | reading up/down flips every weld to the wrong face |
| 2 | single line, title block says ISO 2553 System B | below = arrow side, above = other side; size letters still ISO (a/z/e) | same side rule as AWS but different letters |
| 3 | single line, title block says AWS A2.4 | below = arrow side; bare numbers are legs | reading a bare leg as an ISO throat undersizes welds |
| 4 | single line, no standard declared | unresolved — send an RFI: standard + system + units | guessing wrong flips a whole batch |
| 5 | drawing says ISO 2553 but neither A nor B | non-conforming — ask the customer to add A or B | ISO forbids mixing A and B (S1) |
| 6 | Ø on a plug/spot symbol | pre-2020 AWS habit or non-AWS practice — 2020 removed Ø from the symbol but sizes still use Ø | reading an old drawing as 2020 |
How many spot welds at 50 mm pitch over 1 m?
21 spots if both ends are included — 20 intervals of 50 mm. Counting elements is always intervals plus one; the same arithmetic that sank the intermittent-fillet example.
| Item | Value |
|---|---|
| Intervals in 1000 mm at 50 mm pitch | 20 |
| Spots (both ends welded) | 20 + 1 = 21 |
| Notation | AWS pitch 50; ISO equivalent n × (50) with d noted separately |
What is the AWS effective throat of a flare-bevel weld with R = 12 mm, GMAW?
5/16 × R = 3.75 mm — the D1.1 prequalified effective-throat coefficient for GMAW/FCAW-G (the exact table number varies by edition; the source page is pending re-verification against D1.1). No edition of D1.1 gives 5/8 R for flare-bevel:
| Flare joint | Process | Effective throat | At R = 12 mm | Status |
|---|---|---|---|---|
| Flare-bevel | GMAW / FCAW-G | 5/16 × R | 3.75 mm | D1.1 prequalified effective-throat table (table number varies by edition); source page pending re-verification |
| Flare-V | — | 1/2 R or 3/8 R (per edition) | 6.0 mm or 4.5 mm | verify the coefficient in the edition you buy |
| Flare-bevel — the 5/8 R claim | — | — | — | corrected: no D1.1 edition supports 5/8 R for flare-bevel |
Is a stud weld symbol side-significant?
No — arrow-side only: one side, size left, pitch right, count below in parentheses. Contrast with the neighbours:
| Symbol | Side significance | Dimension positions |
|---|---|---|
| Stud weld (circle-X) | arrow side ONLY — no other-side usage | size left, pitch right, count below in brackets |
| Spot weld (hollow circle) | symmetric — no arrow/other-side meaning | size left, pitch right, count in brackets |
| Fillet weld (triangle) | fully side-significant — the most misread symbol on any drawing | size left, length/pitch right |
What does an empty tail mean in AWS A2.4?
0 specification references — the tail carries process/WPS info only when present; an empty tail is a deliberate no-reference statement, not an omission:
| Tail content | ISO reading | AWS reading |
|---|---|---|
| 135 / ISO 5817-B / PF | process 135 (MAG, ISO 4063) / quality level B / welding position PF | not used — AWS tails carry WPS/spec references |
| a WPS or spec number | possible but unusual — ISO uses 3-digit process numbers | the normal use: WPS / specification / reference |
| empty | no auxiliary requirement stated | 0 references — no spec applies to this weld as drawn |
| basic welding symbol (no joint) | tail is REQUIRED — it carries the only information | — |
What do the dimension letters a, z, s, p, R and b mean?
They are system-bound — copying a letter across systems is the number-one misreading source this page logs. Decode before measuring:
| Letter | ISO 2553:2019 | AWS A2.4:2020 | GB/T 324-2008 (ISO 1992 line) | Conflict | Source |
|---|---|---|---|---|---|
| a | nominal throat thickness (fillet) | not used — bare number = leg | not used (S = effective thickness) | C2 | S1, S16, S13 |
| z | leg length | not used | not used (K = leg) | C2 | S1, S13 |
| s | penetration depth (butt); deep-penetration throat on fillets | not used | not used (H = depth, S = effective thickness) | C2 | S1, S16, S3, S13 |
| S | not used | fillet leg size; in (S) = weld size / effective throat | effective throat thickness | C2, C5 | S4, S6, S13 |
| D | not used | groove depth (since 2012) | not used (H = depth) | C5 | S10, S6 |
| E | not used | pre-2012 effective throat, written (E) | not used | C5 | S10 |
| d | diameter: spot / stud / plug | diameter: spot / plug / stud | spot-weld nugget diameter | — | S1, S11, S13 |
| c | seam weld width; slot width | not used (S / R instead) | weld width | — | S1, S11, S13 |
| root face | depth of root face — current letter unverified (declared gap) | root face by note — no unified letter | p (root face) | C4, G2 | S1, S6, S13 |
| e | distance between weld elements (clear gap) | not used (pitch instead) | weld spacing | C3 | S1, S11, S13 |
| l | length of one weld element | length (left of the hyphen) | weld length | C3 | S1, S6, S13 |
| n | number of weld elements | not used (count in brackets) | number of elements | C3 | S1, S11, S13 |
| p | not used (e instead) | pitch (centre distance) | root face | C4 | S1, S6, S13 |
| P | not used | pitch | not used | C4 | S6 |
| L | not used | length (length-pitch notation) | not used | C3 | S6 |
| R | root radius (U / J) | root opening | root radius | C9 | S1, S6, S13 |
| b | root gap | not used (R instead) | root gap | C9 | S1, S7, S13 |
| α | included angle | groove angle | groove angle | — | S1, S6, S13 |
| K | not used | not used | leg size | C2 | S13 |
| H | not used | not used | groove depth | C5 | S13 |
| h | not used | not used | weld face (reinforcement) | — | S13 |
| N | not used | not used | number of identical welds (in the tail) | — | S13 |
What do the supplementary symbols and tail marks mean?
Flat/convex/concave shapes, all-around circles, field flags, backing, spacers and finish letters ride on the basic symbol — and the 2020 AWS edition reshuffled two of them:
| Supplementary item | ISO 2553 | AWS A2.4 | Meaning | Reading note |
|---|---|---|---|---|
| Flat contour | supplementary No.1 | flat (fillets only) / flush (other welds, 2020) | surface flush with the plate | 2020 split flat vs flush by weld type |
| Convex | No.2 | convex | surface bulges | drawn above the symbol |
| Concave | No.3 | concave | surface hollows | drawn above the symbol |
| Smooth blend | No.4 | no separate symbol (note) | toes ground to a smooth transition | ISO-only graphic; AWS by note |
| Weld-all-around | No.10 | circle at the elbow | weld continues around the joint | circle sits at the arrow-line/reference-line junction |
| Field weld | No.12 | flag at the elbow | welded on site, not in the shop | same junction position as all-around — meaning differs |
| Backing run / back weld | No.5 | §7.7 backing / back weld | a seal pass welded from the far side | backing run is welded; a backing strip is a part |
| Permanent backing | No.7a | backing (permanent) | strip stays in the joint | symbol on the far side of the groove |
| Removable backing | No.7c | removable backing (note) | stripped after welding | distinguish from permanent |
| Spacer | No.8 | spacer | insert controlling the root gap | drawn at the joint |
| Consumable insert | No.9 | consumable insert | root insert becomes weld metal | drawn at the root |
| Melt-through | — | filled half-circle | full penetration visible on the far side | filled vs open half-circle is the AWS distinction |
| Finish designator | note / tail | C G H M P R U | C chipping, G grinding, H hammering, M machining, P planing, R rolling, U unspecified | above the symbol or in the tail |
| Tail | process / standard / quality / position, slash-separated | WPS / spec / reference | the auxiliary-information slot | empty = no reference (0 references) |
| Multiple reference lines | sequence / multiple passes | operation order | read in line order | top-down or as annotated |
| Staggered intermittent welds | Z mark on the line | offset symbols above/below | alternating elements on the two faces | do not confuse the ISO Z with a Z-groove |
How do you read a welding symbol left to right?
Decide the side from the line (solid/dashed or below/above), take the size from the left figure, take length/count/process from the right and the tail. The worked notations below use [solid]/[dashed]/[above]/[below] for symbol position:
| No. | Notation (described) | System | Literal reading | Meaning |
|---|---|---|---|---|
| 1 | [solid] a5 triangle | ISO A | triangle on the solid line; a5 on its left | arrow-side fillet, throat 5 mm |
| 2 | [dashed] a5 triangle | ISO A | triangle on the dashed line | other-side fillet, throat 5 mm |
| 3 | [solid] z6 triangle | ISO A | z6 on the solid line | arrow-side fillet, leg 6 mm |
| 4 | [below] 6 triangle | ISO B or AWS | triangle below a single line; bare 6 on the left | arrow-side fillet, leg 6 mm (AWS S = 6) |
| 5 | [above] 6 triangle | ISO B or AWS | triangle above the line | other-side fillet, leg 6 mm |
| 6 | [below] V 60° s10 | ISO B | V below the line, 60° on the symbol, s10 left | arrow-side single-V, 60° included, penetration 10 mm |
| 7 | [above] V 60° D12(S10) | AWS | V above the line; D12 left, (S10) following | other-side single-V, 12 mm deep, 10 mm effective throat |
| 8 | [below] and [above] V (two) | ISO A/B or AWS | mirrored pair | double-V — weld both sides, no side meaning |
| 9 | [below] circle d6, n × (50) | ISO B | hollow circle centred; d6 left; n × (50) right | spot series: 6 mm nuggets, count and 50 mm spacing per the right-hand notation |
| 10 | [below] rectangle d10 (8) | ISO B | rectangle below; d10 left; (8) inside | plug weld: 10 mm hole, 8 mm fill (omit the depth = fill flush) |
| 11 | [below] wavy line | ISO B or AWS | wavy line below | surfacing / wear layer |
| 12 | [below] three parallel lines | ISO B | three short vertical lines below | edge weld |
| 13 | [below] two flaring lines | ISO B | outward-flaring pair below | flanged edge weld, fully melted |
| 14 | [below] triangle + circle at the elbow | both | circle at the arrow/reference junction | arrow-side fillet, welded all around |
| 15 | [below] triangle + flag at the elbow | both | flag at the junction | arrow-side fillet, field weld |
| 16 | [tail] 135 / ISO 5817-B / PF | ISO | forked tail, slash-separated | process 135 (MAG), quality B (ISO 5817), position PF |
| 17 | two reference lines, symbols on each | AWS | two parallel reference lines | operations in line order (multi-pass sequence) |
| 18 | [below] triangle 6-75/150 | AWS | 6 left of the triangle; 75-150 right | intermittent arrow-side fillet: leg 6, 75 mm elements at 150 mm pitch |
What does p mean — pitch, gap or root face?
All three, depending on the system: AWS p = pitch (centre distance), ISO uses e for gap and has no p, and GB/T 324 p = root face. Ask which standard governs the drawing before translating the letter:
| Document | p means | Applies to |
|---|---|---|
| AWS A2.4 | pitch — centre-to-centre | AWS intermittent, spot and plug series |
| ISO 2553 | not used — clear gap is e | ISO intermittent notation |
| GB/T 324-2008 | root face | Chinese national standard / old ISO-1992-line drawings only |
| shop speech | often pitch, written casually | fine for conversation — never for drawing interpretation |
How to Use These Numbers
- Identify the system first, always: System A reads line type, System B and AWS read up/down — mixing them puts welds on the wrong face of the joint, and ISO forbids mixing A with B on one drawing.
- ISO a = throat, z = leg, AWS bare number = leg: a6 built as a 6 mm leg loses 29.3% of throat and 50% of section. Convert with z = a√2 before anyone strikes an arc.
- AWS D(S) belongs to 2012-and-later editions; older drawings write S(E) — check the edition before reading a groove callout.
- The flare-bevel effective throat is 5/16 × R for GMAW/FCAW-G per the D1.1 prequalified effective-throat table (table numbers move between editions); the source page for that coefficient is pending re-verification against the purchased standard.
- ISO intermittent n × l (e) counts clear gaps; AWS length-pitch counts centres — pitch = l + e. On a 6 m beam, misreading 150 as a gap drops the weld from 40 to 27 elements (−32.5%).
- Undimensioned ISO butt welds default to full penetration; AWS requires CJP to be stated explicitly — neither standard lets you read partial penetration into a blank.
- Declared gaps: the ISO stud-weld official graphic and the current ISO root-face letter could not be verified from accessible sources; text descriptions stand in until the purchased ISO 2553:2019 closes them.
- D1.1 minimum fillet legs are quoted from a secondary digest in rounded millimetres (3/16 in shown as 5 mm; exact 4.76 mm) — verify against the purchased edition.
Frequently Asked Questions
In AWS A2.4, is a weld symbol above the reference line on the arrow side or the other side?
Other side — below = arrow side, above = other side; two positions, one rule (§6.1).
Other side — below = arrow side, above = other side; two positions, one rule (§6.1).
How much throat thickness is lost if an ISO a6 fillet is fabricated as a 6 mm leg?
Throat drops 6.00 → 4.24 mm (−29.3%); area 36 → 18 mm² (−50%).
Throat drops 6.00 → 4.24 mm (−29.3%); area 36 → 18 mm² (−50%).
What leg length satisfies an ISO a5 throat?
z = 5 × 1.414 = 7.07 mm; z7 gives 4.95 mm, z8 gives 5.66 mm.
z = 5 × 1.414 = 7.07 mm; z7 gives 4.95 mm, z8 gives 5.66 mm.
What does AWS 12(10) mean?
Groove depth D = 12 mm, effective throat (S) = 10 mm — 83.3% of the depth.
Groove depth D = 12 mm, effective throat (S) = 10 mm — 83.3% of the depth.
How many weld elements does AWS 75-150 produce on a 6000 mm beam?
40 per side, 3000 mm total — 50% of the member.
40 per side, 3000 mm total — 50% of the member.
If 150 is misread as ISO edge-to-edge e, how many elements result?
27 per side, 2025 mm total — 975 mm (−32.5%) short.
27 per side, 2025 mm total — 975 mm (−32.5%) short.
What is the minimum AWS D1.1 fillet leg for 10 mm plate?
3/16 in = 5 mm (T over 6 mm up to 12 mm; rounded value).
3/16 in = 5 mm (T over 6 mm up to 12 mm; rounded value).
What is the minimum AWS D1.1 fillet leg for 25 mm plate?
5/16 in = 8 mm (T over 20 mm).
5/16 in = 8 mm (T over 20 mm).
How wide is a 60° V groove at 12 mm depth with a 2 mm root gap?
Top width 15.86 mm; area 107.1 mm² ≈ 107.1 cm³ of filler per metre.
Top width 15.86 mm; area 107.1 mm² ≈ 107.1 cm³ of filler per metre.
Does an undimensioned ISO butt weld mean partial penetration?
No — zero dimensions = full penetration by default (Table 1 footnote b).
No — zero dimensions = full penetration by default (Table 1 footnote b).
Can ISO System A and System B be mixed on one drawing?
No — one system per drawing; the drawing must state system and units.
No — one system per drawing; the drawing must state system and units.
How many spot welds at 50 mm pitch over 1 m?
21 spots with both ends included — 20 intervals of 50 mm.
21 spots with both ends included — 20 intervals of 50 mm.
What is the AWS effective throat of a flare-bevel weld with R = 12 mm, GMAW?
5/16 × R = 3.75 mm — D1.1 prequalified coefficient for GMAW/FCAW-G (table number varies by edition).
5/16 × R = 3.75 mm — D1.1 prequalified coefficient for GMAW/FCAW-G (table number varies by edition).
Is a stud weld symbol side-significant?
No — arrow-side only; 1 side, size left, pitch right, count below in parentheses.
No — arrow-side only; 1 side, size left, pitch right, count below in parentheses.
What does an empty tail mean in AWS A2.4?
0 specification references — the tail carries process/spec info only when present.
0 specification references — the tail carries process/spec info only when present.
Standards & Sources
- S1 — ISO 2553:2019 official page and iTeh preview PDF (system definitions, terms, clause titles, Table 1 footnote b)
- S2 — ISO 2553:1992 iTeh preview PDF (clause 5.4 vertical reference lines, clause 5.5 solid/dashed rule)
- S3 — TWI, A review of the application of weld symbols on drawings (a/z/s definitions, intermittent elements, Z stagger, ISO 4063 process numbers)
- S4 — AWS A2.4:2020 product page (ANSI webstore; 8th edition)
- S5 — AWS Inspection Trends May 2025 (arrow-side clause 6.1 quoted verbatim)
- S6 — clause5.io A2.4 reference and ISO comparison (clause index, D(S), flare coefficients — pending re-verification against D1.1)
- S7 — DoaWise, Reading Welding Symbols and Fabrication Drawings (plug/slot, AWS preparation, tail order, CJP/PJP)
- S8 — WeldFC Academy, ISO 2553 complete guide (symbol shapes corroboration)
- S9 — wpswelding, Minimum Fillet Weld Size per AWS D1.1 (secondary digest, rounded mm)
- S10 — AWS A2.4:2012 ANSI preview PDF (S(E) → D(S) change of edition)
- S11 — ISO 2553:2013 third-party Chinese translation (Table 1 numbering, clauses 5.6–5.11 corroboration)
- S12 — ANSI Blog, Changes to AWS A2.4:2020 (spot/seam left-side values, Ø removal)
- S13 — GB/T 324-2008 weld symbols (letter set p/K/H/S corroboration)
- S14 — ISO 9692-1:2013 official page (groove preparation standard, existence and scope)
- S15 — clause5.io AWS Symbols Hub (spot/seam/stud/edge/surfacing/backing shapes)
- S16 — ISO 2553:2019 OBP terminology (arrow side, nominal throat thickness, s)
Related Pages
- /wiki/sheet-metal/welding-distortion-control/ — Keeping welded sheet metal straight while the symbols are being honoured
- /wiki/sheet-metal/design-for-sheet-metal/ — DFM rules that decide which weld types a sheet-metal part can carry
- /wiki/sheet-metal/tolerance-and-surface/ — Tolerances and finish expectations for welded assemblies