AWS A2.4 weld symbol
J-Groove Weld Symbol
A J-groove weld symbol is half a U, calling for a curved preparation on only one member — the broken leader line points at the member to be prepared.
How to read the j-groove weld symbol
- Only one member is prepared, with a curved J-shaped groove.
- The leader line is broken and points at the member that gets the preparation.
- The vertical leg of the symbol is always drawn on the left.
- Groove angle outside the symbol, root opening inside.
- A J above and below the reference line calls for a double-J joint.
Where the dimensions go
| Position | What it specifies |
|---|---|
| Inside the symbol | Root opening |
| Outside the symbol | Groove angle |
| Left of the symbol | Depth of bevel, with groove weld size in parentheses |
Joint types
- Butt joint
- T-joint
- Corner joint
Practical notes
- J-grooves are used on thick T-joints and corner joints where only one member can be prepared.
- Like the U-groove, the payoff is a large reduction in filler metal on heavy sections.
- The curved root gives better electrode access than a straight bevel of the same narrow angle.
J-Groove Weld symbol — common questions
What does a J-groove weld symbol look like?
Half of a U: a straight vertical leg on the left and a curved leg on the right, drawn on the reference line with a broken leader pointing at the member to be prepared.
Why is the leader broken on a J-groove symbol?
Because only one member is prepared. The break in the leader line identifies which one, exactly as it does on a bevel-groove symbol.
When would you use a J-groove instead of a bevel-groove?
On thick material. The J prep uses considerably less filler metal than a straight bevel of equivalent access, which matters once the section gets heavy enough to justify the machining.
Can a J-groove be welded from both sides?
Yes — a J drawn above and below the reference line specifies a double-J preparation, welded from both sides to balance distortion.
Welding symbol anatomy
Every weld symbol attaches to the same framework. If any part of the diagram above is unfamiliar, the full guide to reading welding symbols walks through the whole system.
| Reference line | The horizontal backbone of every welding symbol. Everything else attaches to it, and it is always drawn horizontal on the drawing. |
|---|---|
| Arrow | The leader and arrowhead that connect the reference line to the joint. The side of the joint the arrow touches is the arrow side. |
| Weld symbol | The shape that says which kind of weld is required — triangle for a fillet, V for a V-groove, circle for a spot, and so on. |
| Arrow side (below the line) | A weld symbol drawn below the reference line calls for a weld on the side of the joint the arrow points to. This is the convention that catches people out most often. |
| Other side (above the line) | A weld symbol drawn above the reference line calls for a weld on the far side of the joint. |
| Both sides | Symbols drawn above and below the reference line call for welds on both sides of the joint. |
| Tail | An optional fork at the far end of the reference line, used to reference a specification, process or procedure such as GMAW or a WPS number. |
| Dimensions | Size is placed to the left of the weld symbol; length and pitch are placed to the right. |