In an AWS A2.4 welding symbol, a weld symbol below the reference line means weld on the arrow side of the joint, above the line means the other side, and on both sides means both. The size goes to the left of the weld symbol and the length and pitch to the right, on whichever side the weld is.
A welding symbol is built from a horizontal reference line, an arrow that touches the joint, an optional tail for the process or specification, and the weld symbol itself with its dimensions. Symbols read left to right whichever end the arrow is on, and the perpendicular leg of fillet, bevel and J symbols is always drawn on the left. This chart shows each basic and supplementary symbol as it is drawn, where every dimension goes, five worked examples, and how ISO 2553 differs. To size a fillet from its throat, use the fillet weld calculator.
Arrow side and other side
The arrow side is the side of the joint the arrow touches. For bevel and J grooves, where only one member is prepared, the arrow line has a break that points at the member to be prepared, unless the drawing makes it obvious. Resistance spot and seam welds have no arrow or other side, so their symbols sit centred on the line.
Basic weld symbols
| Symbol | Drawing | Meaning and dimensions |
|---|---|---|
| Groove welds | ||
| Square groove | Two parallel lines. Butt joint with no edge preparation; root opening goes between the lines. | |
| V-groove | Both members bevelled. Groove angle is written outside the V, root opening inside. | |
| Bevel groove | Only one member is bevelled. The vertical leg is always drawn on the left; a break in the arrow line points to the member that gets the bevel. | |
| U-groove | Both members prepared with a radiused (J) edge. Thick plate, less weld metal than a V. | |
| J-groove | One member prepared with a radiused edge. Vertical leg on the left; arrow break points to the prepared member. | |
| Flare-V groove | Joint between two rounded surfaces, such as two tubes or two bent edges. | |
| Flare-bevel groove | Joint between a rounded surface and a flat one, such as a bar or tube on a plate. | |
| Fillet, plug, slot, spot, seam and others | ||
| Fillet | Right triangle, perpendicular leg always on the left whichever way the joint faces. Size to the left, length and pitch to the right. | |
| Plug or slot | Rectangle. The hole or slot is in the member on the arrow side when the symbol is below the line. Hole diameter (or slot width) to the left, fill depth inside. | |
| Spot or projection | Circle. Centred on the line for resistance spot welds, which have no arrow or other side. Size or strength to the left, pitch to the right, number of welds in brackets. | |
| Seam | Circle with two lines through it. Centred on the line for resistance seam welds; width to the left, length and pitch to the right. | |
| Stud | Circle with a cross, arrow side only. Stud diameter to the left, pitch to the right, number of studs in brackets. | |
| Back or backing weld | Half circle on the side opposite the groove symbol. Use the tail or the welding sequence to show whether it is a back weld (made after) or a backing weld (made first). | |
| Surfacing | Two half circles, arrow side only. Build-up or hardfacing; the figure to the left is the minimum thickness of the deposit. | |
Also in AWS A2.4: the scarf groove (two parallel slanted lines, mostly used for brazing) and the edge weld symbol for welds on the edges of flanged or butting members. They are rarely seen on general fabrication drawings, so they are not drawn here; see the standard.
Supplementary symbols
| Symbol | Drawing | Meaning and dimensions |
|---|---|---|
| Weld all around | Circle where the arrow meets the reference line. The weld goes right round the joint, for example a tube to a plate. | |
| Field weld | Flag at the junction: the weld is made on site or at installation, not in the shop. | |
| Melt-through | Filled half circle on the side opposite the groove symbol: visible root reinforcement is required from a one-sided weld. Height of reinforcement to the left. | |
| Consumable insert | Square on the side opposite the groove symbol. The insert class (AWS A5.30) goes in the tail. | |
| Backing | Rectangle on the side opposite the groove symbol. M = backing material specified in the tail; MR = removable after welding. | |
| Spacer | Rectangle on the reference line inside a double groove symbol; the spacer material goes in the tail. | |
| Contour: flush or flat | Straight line beyond the weld symbol: weld face finished flush or flat. | |
| Contour: convex | Arc bowing away from the weld symbol: convex face. | |
| Contour: concave | Arc bowing towards the weld symbol: concave face. | |
| Finishing method | Letter beyond the contour symbol: C chipping, G grinding, H hammering, M machining, P planishing, R rolling, U unspecified. |
Where the dimensions go
| Mark | Meaning | Position |
|---|---|---|
| S | Depth of groove preparation, or size of a fillet, plug or spot weld | Left of the weld symbol |
| (E) | Groove weld size (effective throat), in brackets after S | Left of the weld symbol |
| R | Root opening; for plug and slot welds, depth of filling | Inside the weld symbol |
| A | Groove angle, or included countersink angle of a plug weld | Outside the weld symbol, beyond the root opening |
| L | Length of weld (omitted for a continuous full-length weld) | Right of the weld symbol |
| P | Pitch: centre-to-centre spacing of intermittent welds | Right of the length, after a hyphen |
| Contour | Flush, convex or concave symbol | Beyond the weld symbol |
| F | Finishing method letter (C, G, H, M, P, R, U) | Beyond the contour symbol |
| (N) | Number of spot, seam, stud, plug or projection welds | Above or below the weld symbol, in brackets |
| T | Specification, process (e.g. GMAW, SMAW) or other reference; a closed tail holds a specific note | Tail (omit the tail when nothing is referenced) |
Elements on the other side are placed the same way above the line. The positions stay the same when the arrow is on the right-hand end of the reference line: size still reads to the left, length and pitch to the right. Dimensions are in the drawing's units; mixed units are marked.
Worked examples
Example 1: 6 mm fillet weld, both sides, continuous
A fillet triangle on both sides of the line means a fillet on the arrow side and the other side of the joint (for example both sides of a T-joint). The 6 to the left of each is the leg size. With no length on the right, the weld runs the full length of the joint.
Example 2: 6 mm fillet, both sides, chain intermittent 50-150
Same fillet both sides, but intermittent: welds 50 mm long at 150 mm pitch (centre to centre), so the gap between welds is 100 mm. The symbols are directly opposite each other, so the welds on the two sides line up (chain intermittent).
Example 3: 6 mm fillet, both sides, staggered intermittent 50-150
Offsetting the two symbols along the line means staggered intermittent: the welds on the other side fall midway between the welds on the arrow side. Size, length and pitch are read the same way.
Example 4: Single-V groove, 60°, 2 mm root opening, back weld, ground flush
V on the arrow side with the 2 mm root opening inside the symbol and the 60° groove angle outside it. The flush contour and G mean the weld face is ground flush. The half circle on the other side is a back weld made after the groove weld. No S(E) means a complete joint penetration weld. The tail gives the process, SMAW.
Example 5: 5 mm fillet all around, field weld, GMAW
Circle = weld all around (for example a tube or post to a base plate); flag = made in the field. A 5 mm fillet on the arrow side, process GMAW in the tail.
ISO 2553 differences
- Dashed identification line (system A). ISO 2553 adds a dashed line parallel to the reference line, above or below it. A symbol on the solid line means the arrow side; a symbol on the dashed line means the other side. Symmetrical welds on both sides drop the dashed line. ISO 2553 system B works like AWS (below = arrow side, no dashed line).
- Fillet size letter. ISO writes a for the throat thickness or z for the leg length before the number (a5, z7). AWS gives the leg size alone.
- Intermittent welds. ISO writes number × length (gap), for example a5 3 × 50 (100), where 100 is the gap between welds. AWS gives length-pitch, and pitch is centre to centre.
- Process numbers. The ISO tail uses ISO 4063 numbers: 111 manual metal arc (SMAW), 135 MAG with solid wire, 136 flux-cored with active gas, 141 TIG.
Check which system a drawing uses before reading it. A European drawing with a dashed line is ISO system A; reading it as AWS can put the weld on the wrong side.
Shop tips
- A fillet size with no length means full length, between abrupt changes in direction unless the all-around circle is shown.
- If a groove symbol has no S(E), the weld is complete joint penetration (CJP).
- Length-pitch: the pitch is centre to centre. On 50-150, the gap between welds is 100, not 150.
- Notes, process and filler references in the tail apply to the whole symbol. If the tail is missing, look for a general note on the drawing.
Related calculators and charts
Source: AWS A2.4, Standard Symbols for Welding, Brazing, and Nondestructive Examination, and ISO 2553 (welding and allied processes, symbolic representation on drawings). Symbols are drawn to the standard's conventions but not to scale. Where a drawing, WPS or contract specifies a standard edition, follow that edition.