This is one of the chainplates, 4 mm AISI 316. This material eats up drills like a wonder. MUST keep the drill bit cooled, also the metal below, keep the RPM down and add lots of oil. If I could, I’d put a constant flow of oil into the drilling hole. On the two chainplates, I used up about 4 drill bits. I do not have the means to sharpen drills. It can probably also be done on a dremel, but I do not have the theoretical skill. SHould look it up…