Square groove weld symbol

The square groove symbol is a pair of straight lines perpendicular to the reference line. There is no angle to read because nothing is bevelled: the two members meet edge to edge with their as-cut faces square to the plate surface. All the preparation information is therefore in one place, the root opening, which is written between the two lines.

The root opening is the deliberate gap left between the two square edges before welding. On thin material a zero or near-zero gap is normal because the arc can reach the far side unaided. As thickness climbs, the gap has to open up so the first pass can fuse to the root instead of bridging across it, which is why square grooves are usually confined to the thinner end of the plate range.

A number to the left of the symbol is the groove weld size — how deep the joint is actually filled. On a square groove welded from one side only, that size is measured from the face down to where fusion stops, and it may be less than the plate thickness. Where the joint is welded from both sides, a symbol appears above and below the reference line and each carries its own depth.

Because the square groove has no bevel to guide the eye, fit-up is what makes or breaks it. Tight in one spot and wide in another and the same travel speed will burn through at the gap and leave incomplete fusion where it closed up. Inspectors reading this symbol usually check the gap along the whole seam before any arc is struck.