Might that drill bit size be 27/64ths? I think that is the correct denominator. Never heard of a 63.
Aren't you a machinist? You could just make a cylinder and then drill and tap the top of it for a bolt rather than what Bosch did with the stud. You could even make it from aluminum until you find the profile you like then make a steel one.I thought of that, figured I'd start with a "known" value. Who knows, it might be just right although it looks to steep at the beginning.