Welding Symbols (ISO 2553 / JIS Z 3021)
This chart explains the names, forms and uses of basic and supplementary weld symbols under ISO 2553/JIS Z 3021. Identify the weld type first, then use its position above or below the reference line to determine the weld side.
Butt / groove welds| Weld type | Japanese | Symbol form | Meaning / use |
|---|
| Square (I) butt | I形 | Two parallel edges | Butt weld on thin plate, no bevel. |
| V-groove butt | V形 | A ‘V’ | Both edges bevelled into a V, welded from one side. |
| Single-bevel butt | レ形 | Half-V (レ) | Only one edge is bevelled. |
| U-groove butt | U形 | A ‘U’ | U bevel for thick plate, less filler. |
| J-groove butt | J形 | A ‘J’ | J bevel on one edge, thick plate. |
| Double-V (X) butt | X形 | Two opposed V's | V bevel on both faces, less distortion. |
| Double-bevel (K) butt | K形 | Two half-V's | One edge bevelled on both faces. |
| Flare groove | フレア形 | A curved edge | Weld on a rounded edge (tube, folded sheet). |
Fillet and other welds| Weld type | Japanese | Symbol form | Meaning / use |
|---|
| Fillet weld | すみ肉 | Right triangle (△) | T, corner or lap joints — the most common weld. |
| Plug / slot weld | プラグ / スロット | Filled hole / slot | Weld through a pre-cut hole or slot in the top plate. |
| Spot weld | スポット | A circle (○) | Spot weld (resistance or arc). |
| Seam weld | シーム | A circle with a line | Continuous seam joining lapped sheets. |
| Surfacing / build-up | 肉盛 | Two arcs | Build up dimension or add a surface layer. |
Supplementary symbols| Weld type | Japanese | Symbol form | Meaning / use |
|---|
| Weld all around | 全周溶接 | Circle ○ at the arrow bend | Weld around the entire joint contour. |
| Field weld | 現場溶接 | A flag at the arrow bend | Welded on site at assembly, not in the shop. |
| Surface shape | 平ら / 凸 / 凹 | Flat line / convex / concave arc | Requires a flat, convex or concave weld face. |
| Finishing method | C / G / M / F | A letter by the surface symbol | C: chipping · G: grinding · M: machining · F: other. |
Most weld symbols have NO standard font glyph, so the table describes them by name and shape — read the name/form columns. Position rule: a symbol BELOW the reference line = weld the arrow side (手前); ABOVE = the other side (向こう). Throat/section (a/S), length (L) and pitch (P) come from the drawing. This table only explains the symbols.
Frequently asked questions
What does a symbol below the reference line mean?
Under the convention shown in the chart, a symbol below the reference line indicates the arrow side; one above indicates the other side. Check the diagram and matching symbol row.
Where do dimensions a, S, L and P come from?
Throat or section, length and pitch come from the specific drawing. This chart identifies symbol meaning; it does not derive weld dimensions.
Why does the chart describe symbol shapes instead of using font glyphs?
Many weld symbols lack reliable standard font glyphs and may render differently across devices. Use the chart's weld-name and symbol-form columns together with the diagram.
MINATA — minatavn.com