Hi, I own a lot of old safes and can guarantee that many makers used their own particular threads for fasteners. I have an old Victor vault door that when I was installing it I broke off a bolt and it turned out to be a .725 X 9 ½ TPI thread. I also just walked down stairs and grabbed an original acorn off a 1906 Mosler safe and it is a ⅝″ X 10 TPI. So many makers like Henry Ford, only wanted their parts and technicians working on their units.