J-groove weld symbol

The J-groove symbol is drawn with a straight perpendicular leg on the left and a curved face on the right, which is exactly half of the U symbol. It says one member is prepared with a radiused groove and the other is left square, the same single-sided idea as a bevel groove but with a curved profile instead of a straight cut.

As with any single-member preparation, the symbol cannot say which physical member is cut, so the leader is normally drawn with a break that swings toward the prepared piece. On a tee joint that is usually the attached member, on a butt joint between unequal thicknesses it is usually the thicker one, but read the break rather than guessing from the geometry.

The angle beyond the curved face is that face's angle off the plate surface, and on a J it is small for the same reason it is small on a U: the root radius, not the angle, gives the electrode room at the bottom. The root opening sits inside the symbol, the depth of preparation sits to the left, and the root radius normally appears on the joint detail rather than on the symbol.

J preparations earn their machining cost on thick single-sided joints where a straight bevel would open into a very wide groove. They also produce a gentler transition at the root than a sharp bevel, which matters where the joint sees fatigue loading and where a sharp root corner would concentrate stress.