Welding Symbols ISO 2553: Reading Technical Drawings
What are welding symbols for?
In structural metalwork technical drawings, each weld is represented by a standardised symbol that tells the welder and inspector everything needed: groove type, dimensions, process and finish requirements.
The governing standard in Europe is ISO 2553 (EN ISO 2553).
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The reference line
Every welding symbol is built on a reference line consisting of:
- Continuous line — arrow side
- Dashed line — other side (optional for symmetrical welds)
- Arrow — points to the joint
- Tail — optional, for supplementary information
Fundamental rule: a symbol below the continuous line means the weld is on the side the arrow points to.
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Elementary weld symbols
| Symbol | Type |
|---|---|
| ─── | Square butt (I groove) |
| V | V groove |
| X | Double V groove |
| U | U groove |
| J | J groove |
| △ | Fillet weld |
| ○ | Spot weld |
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Dimensions on the symbol
| Position | Information |
|---|---|
| Left | a = throat thickness or z = fillet leg |
| Right | l = weld length |
| Bottom right | (e) = pitch (intermittent welds) |
a vs z: a = z × cos 45° ≈ 0.7 × z. ISO 2553 uses a as the primary notation.
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Supplementary symbols
| Symbol | Meaning |
|---|---|
| ⌒ | All-around |
| ● | Site weld |
| ▽ | Flush finish |
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The tail
- `135` = MIG/MAG (ISO 4063)
- `111` = Manual Metal Arc
- `B` = Quality level B (EN ISO 5817)
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Most common errors
- Confusing a with z
- Ignoring the dashed line
- Not checking arrow direction
- Omitting length on intermittent welds
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