Martin,
If you have a set of drill bits in 64th increments just try filling a drill into the hex. It should give you a rough idea. A drill bit will be undersized a few thou but if a 15/64 bit doesn't fit you'll know that's not the answer either.
Check that your 7/32 Allen wrench is not rounded off at the end and grind it flat it needed.? rounded corners can make it fell sloppy. 15/64 just seems like a very odd dimension for manufacturing reasons.
Allen wrenches can be filed, with a sharp file.. but it might? take you awhile. Allen wrench is "toughened"? high 40's low 50's Rc. if they were hard hard they be brittle and break,? Bastard files 60ish Rc.
may the force be with you.
Kevin B.
