Unequal leg fillet weld symbol

Most fillets are dimensioned with one number because both legs are the same. When the design wants a long, shallow weld or a tall, narrow one, two sizes appear to the left of the triangle in the form of one dimension by another. The pair is a description of the triangle's two legs, so a 1/4 by 1/2 fillet has a quarter-inch leg on one member and a half-inch leg on the other.

The notation itself cannot say which leg goes where, because the triangle is always drawn the same way regardless of joint orientation. That information comes from the drawing: a detail view, a dimension on the joint sketch, or a note beside the symbol. Never assume the first number belongs to the vertical member — check the detail, because getting it backwards changes the weld's throat orientation and its behaviour under load.

Unequal legs show up where the two members differ in thickness, where a long leg is wanted to spread load onto a thin plate, or where a taller leg is needed to reach past a radius or a fit-up gap. They also appear in fatigue-sensitive details, since a shallower approach angle at the toe eases the stress concentration where the weld meets the base metal.

Everything else on the symbol reads normally. A length to the right still sets the run, a length-pitch pair still makes it intermittent, and a triangle on each side still means both faces get welded. When both faces carry unequal legs, each side gets its own pair of numbers and each has to be checked against its own detail view.