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Square groove weld symbol: what it means on a drawing

Fillet Gauge editorial teamSources checked 4 min read

The square groove weld symbol is two short parallel strokes standing on the reference line. It calls for a groove weld between members whose edges are left square, with no bevel or other preparation. Below the line it is welded from the arrow side, above the line from the other side, and on both sides from each side.

A butt joint drawn end on: two plates with square, unprepared edges and a small gap between them filled with weld metal, beside a square groove symbol with 1/16 between its two strokes
Two strokes, no bevel. The number between them is the root opening. Numbers are invented.
Use this diagram

How to read it

  1. Find the side. Strokes below the line mean the arrow side of the joint. Above the line, the other side. Strokes on both sides of the line ask for welding from both faces of the same joint, which is common on thicker square butts.
  2. Read between the strokes. A number there is the root opening, the gap you set between the two square edges before welding. 1/16 means a 1/16 gap. No number means the drawing sets no gap on the symbol, so look for a note or a detail.
  3. Read the left side. A number on the left is the weld size, how deep the weld has to fuse into the joint. With nothing on the left of a one-sided groove, read it as complete joint penetration unless a note in the tail says otherwise.
  4. Read the right side. A number on the right is the weld length. With no length, the weld runs the full length of the joint.
  5. Read the tail. The process, a procedure number or a note such as CJP goes there.

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Question 1 of the free 10-question check on CWI Part A. No signup. Then ask Tack, the AI study buddy, why the answer is right and the others are wrong.

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Symbols - Welding and NDE

On a welding symbol, what does a circle at the junction of the arrow and the reference line indicate?

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Why a square groove

Square butts are the cheapest groove to fit up: nothing to cut, grind or machine. They work where the welding process can fuse the full thickness from one or both sides, so you see them on thin plate, sheet and some automated processes. Once the thickness gets past what one pass can fuse, the drawing moves to a V-groove or a bevel.

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Common mix-ups

  • Square groove or edge weld. The edge weld mark has three strokes joined at their outer ends. The square groove has two strokes that are not joined. Count the strokes before you read anything else.
  • Root opening or weld size. The number between the strokes is the gap. The number on the left is the weld size. Swapping them turns a 1/16 gap into a 1/16 weld.
  • Both sides or double-V. Two strokes on each side of the line is still a square groove, welded from both faces. A double-V groove shows a V on each side and needs both members beveled.

Square grooves on the CWI exam

Part A of the CWI exam is closed book, and the symbols domain (Symbols, Welding and NDE) is at least 10% of it, so you need to tell two strokes from three on sight. On Part B, Utilization of Specifications and Drawings is at least 8% of the practical, and the root opening between the strokes is the kind of number you check against a fit-up.

Practice it

Draw a square groove in the welding symbol builder on one side, then both, and read back what changes. Put it next to every other groove shape on the welding symbols chart.

Two strokes sorted? Check the rest of Part A

Take the free 10-question check. It's weighted to the Part A outline, scored by domain and needs no signup, so you see whether symbols or another domain costs you the most points. The Part A course gives you a lesson on reading welding and NDE symbols and on every other exam subject, two full-length timed practice exams, and a worked explanation with every answer.

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Facts checked 24 October 2026 against the sources listed above. If something has changed, tell us and we will correct it within 2 business days.

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