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J-groove weld symbol: what it means on a drawing

Fillet Gauge editorial teamSources checked 3 min read

The J-groove weld symbol is one upright stroke with a curve beside it, like a J on its back. It calls for a groove weld in which only one member gets a curved preparation and the other keeps a square edge. When the arrow has a break, its last segment points at the member that gets the J.

A butt joint drawn end on: the left plate has a square edge and the right plate a curved J preparation, filled with weld metal, beside a J-groove symbol and an arrow with a break pointing at the right plate
Straight leg always on the left. The broken arrow picks the member. Numbers are invented.
Use this diagram

How to read it

  1. Find the side. Below the line, the J is cut and welded from the arrow side. Above the line, from the other side. A J on each side is a double-J, with the same member prepared from both faces.
  2. Find the member. Look for a break, a jog, in the arrow. The segment after the break points at the member that gets the curved preparation. With no break, the symbol doesn't say which member to prepare, and the shop picks unless a note or detail decides it.
  3. Read the left side. Groove depth comes first, then the weld size in parentheses, the same as every other groove.
  4. Read the tail. Like the U, a J is made to a set radius and root face that the symbol doesn't carry. The tail points to the detail or section that does.
  5. Read the right side. A length there limits the weld. No length means the full joint.

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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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The straight leg is always on the left

The J mark is drawn with its upright stroke on the left and the curve on the right, whichever way the arrow points and whichever member is prepared. The same rule holds for the fillet, bevel and flare-bevel marks. So the mark's shape never tells you which member gets the J. Only the arrow break does.

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Common mix-ups

  • J or bevel. Both prepare one member and both use the arrow break. The bevel groove mark has a straight sloping stroke. The J has a curve.
  • J or U. The U-groove mark curves on both sides because both members are prepared. One curve and one upright stroke is a J.
  • Reading the mark's direction. People flip the J to match the joint on the drawing. Don't. Read the arrow break, not the way the curve faces.
  • Break or bend. An arrow that simply leaves the line at an angle isn't broken. A break is a distinct jog partway along the arrow.

J-grooves on the CWI exam

J and bevel marks are easy to swap under time pressure, because the only difference is a curve and the member is set by the arrow. They sit in Symbols, Welding and NDE, at least 10% of closed-book CWI Part A. Part B drawings bring the arrow break back under Utilization of Specifications and Drawings, at least 8% of the practical.

Practice it

The welding symbols quiz puts the J beside the bevel, U and V and explains each answer. Find every groove shape in one place on the welding symbols chart.

Got the J? 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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