I've made a few open end wrenches. A couple for the spindle on my
horizontal mill (1", 1-1/4 or so). I just used 3/16 mild steel.
They're about 8 - 10" long, so it's not possible to put a lot of torque
on the jaws. But on occasion I've whacked one with a lead hammer
without ill effect.

YMMV, of course.

Bob