Оригинал: LEG WELD DETAILS WAS 15 FILLET TO COMP PAD, NOW FILL PEN. CLIENT DETAIL UPDATED.

Знаю только, что comp pad это опорные платики здесь...

Заранее спасибо за помощь

leg weld(ing) = where two sheets of metal are welded together, typically at a right-angle (90 degrees).

leg (here) or cathetus -- see C1 and C2 in figure 1 here:
https://en.m.wikipedia.org/wiki/Cathetus

fillet weld(ing):
"Fillet welding refers to the process of joining two pieces of metal together, either at right-angles or at some other angle. Right-angled (perpendicular) welds are commonly referred to as T- or Tee joints. The weld can be roughly triangular in shape, or curved."

Comp Pad possibly = compensation pad.

pen possibly = penetration??? (in a weld) = the distance by which a weld penetrates the two pieces of metal being welded together -- see figure 2 in
https://en.m.wikipedia.org/wiki/Fillet_(mechanics)