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...