WELDINGResources / Welding symbolsUpdated 29 Oct 2026

Supplementary welding symbols

Supplementary symbols add to the weld symbol: a weld all around the joint, a weld made on site, a backing strip, or the shape of the finished weld face.

SymbolAWS A2.4ISO 2553What it is

Weld all aroundA circle at the junction of the arrow and the reference line means the weld goes all the way around the joint, such as a tube to a plate.

Field weldA flag at the junction of the arrow and the reference line means the weld is made in the field, on site or at installation, not in the shop.

Backing stripA backing strip is a bar or strip under the root of a groove weld that supports the weld metal.

Flush contourA straight line over the weld symbol means the weld face is finished flat, flush with the surface.

Convex contourAn arc bulging away from the weld symbol means the finished weld face is convex.

Concave contourAn arc bulging towards the weld symbol means the finished weld face is concave, usually on fillet welds for a smooth transition.

Supplementary symbols: AWS and ISO

Both standards use a circle at the junction for a weld all around and a flag for a field (site) weld. Contours are drawn the same way: a straight line for flush, an arc for convex or concave.

Backing is marked differently. AWS draws a rectangle opposite the groove symbol, with R inside when the backing is removed. ISO 2553 writes M in the rectangle for a permanent backing strip and MR for a removable one.

Frequently asked questions

Which supplementary symbols appear on a welding drawing?

This legend covers weld all around, field weld, backing strip, flush contour, convex contour, concave contour. Project legends may add more.

Are these symbols different in ISO and AWS?

6 of the 6 are drawn differently. Each symbol page shows both forms side by side.

Can I download these symbols?

Yes. Each symbol page has free SVG files, and the hub has printable PDF charts.

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Supplementary symbols: AWS and ISO

Frequently asked questions

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