GaugePass

Weld symbol

Square groove weld symbol

Two short parallel lines crossing the reference line call for a square groove weld - a butt joint welded with no bevel, where the only preparation is how far apart the two square edges are set.

Interactive drawing

1/81/8
TitleSquare groove symbol
ViewAs drawn
Sheet1 / 2
The symbol as it appears on the drawing
arrowarrow side (this face)other side
TitleSquare groove joint
ViewSection
Sheet2 / 2
The joint it produces, in cross-section

Reads asArrow side: square-groove weld, 1/8 size, 1/8 root opening.

How to read it

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.

Where each dimension goes

Root opening (between the two lines)
The gap set between the two square edges before welding, which is the joint's only preparation.
Groove weld size (left of the symbol)
Depth of the joint that is filled with weld metal, measured from the face inward.
Symbol above and below the line
Welding from both sides. Each side is dimensioned separately with its own depth.
Length (right of the symbol)
Run length where the groove weld does not extend the full seam.

Worked examples

Each one is a drawing, the sentence it comes out as, and then the mark-by-mark account of why. Read the sheet first and say the sentence yourself before you look down.

  1. Square groove welded from both sides

    3/163/161/16
    TitleSquare groove welded from both sides
    RefSquare groove
    Ex1 / 2

    Reads as

    Weld this square butt from both sides, 3/16 deep each side, with a 1/16 root opening.

    Which mark says so

    • square-groove symbolBelow the reference lineA square-groove weld on the arrow side of the joint
    • 3/16Left of the arrow-side symbolGroove weld size - how deep the weld itself goes
    • 1/16Inside the arrow-side symbolRoot opening - the gap left between the members before welding
    • square-groove symbolAbove the reference lineA square-groove weld on the far side of the joint
    • 3/16Left of the other-side symbolGroove weld size - how deep the weld itself goes

    A symbol above and below the line means the joint is welded from each face. The 3/16 on each side is that side's groove weld depth, and the 1/16 between the lines is the fit-up gap.

    And what it does not say

    • No length is given, so each weld runs the full length of the joint.
    • There is no circle at the elbow, so the weld does not continue around the joint.

  2. Square groove with a closed root

    1/80
    TitleSquare groove with a closed root
    RefSquare groove
    Ex2 / 2

    Reads as

    Weld the arrow side square groove 1/8 deep with the edges closed tight.

    Which mark says so

    • square-groove symbolBelow the reference lineA square-groove weld on the arrow side of the joint
    • 1/8Left of the symbolGroove weld size - how deep the weld itself goes
    • 0Inside the symbolRoot opening - the gap left between the members before welding

    A zero root opening means the two square edges are butted with no deliberate gap, which suits thin material where the arc reaches the back face without help.

    And what it does not say

    • No length is given, so each weld runs the full length of the joint.
    • Nothing sits above the reference line, so the far face of the joint stays bare.
    • There is no circle at the elbow, so the weld does not continue around the joint.

Common mistakes

  • Looking for a groove angle that a square groove never has, then assuming the symbol is incomplete.
  • Reading the root opening as a weld size. The number inside the symbol is the fit-up gap, not the depth filled.
  • Using a square groove on material too thick for the arc to reach the root, which leaves incomplete penetration.
  • Letting the gap vary along the seam because there is no bevel to make the inconsistency obvious.

Typical joints

Thin plate butt jointsSheet metal seamsLight pipe and tube buttsSquare-edge corner joints

Related symbols

V-groove weldA V drawn on the reference line calls for a V-groove weld. Both members are bevelled, and the symbol carries three numbers: the included angle, the root opening, and the depth of the groove.Bevel grooveHalf a vee - one vertical leg and one sloped face - means only one member is prepared. A broken arrow points at the member that gets the bevel, because the symbol alone cannot say.Back weldA semicircle opposite a groove symbol calls for a weld deposited on the back of the joint after the groove side is welded, sealing and reinforcing the root from the far face.CJP groove weldCJP in the tail says the weld must fuse through the entire thickness of the joint. The preparation is left to the fabricator, so no groove size appears to the left of the symbol.