dpb wrote:

Have application just begs for carriage bolt...have never seen punch to
create them--presume must exist? Something like a Greenlee but one
piece is 1-1/2 hollow square w/ 1/8" wall so couldn't get in even if
could deal with the thickness.

More than I care to file out by hand...easy alternatives, anybody??? I
suppose could just go on and use a truss head and hold the back side but
it's a stretch to reach all of 'em while trying to tighten...
You can definitely get square punches, I'd guess Greenlee makes them, too.
They'd need to be keyed so the punch aligns with the die.

I have a big old foot-powered punch press and a selection of punches and
dies.

Jon