No the holes are more of a screw countersink shape, and use a 9/32″ ball-bearing in the arm, never a 1/4″ ball. The original plates were hardened steel, and can hardly be marked with a file. As hardening is very expensive these days unless you have a back door contact, perhaps make it from a good piece of boiler-plate, slightly better than mild steel, and then flame-carburize harden it with an acetylene-rich flame from oxy-acetylene welding kit, or use “Casenite” or other proprietary hardening stuff. Not sure of depth of holes as I am hors de combat at the moment…
