I'm trying to get a handle on how to match the caliper adapter to my frame/fork and rotor size. Usually calipers come as post mounts so is the spacing between the two holes the same for all the manufacturers? I mean is there a standard spacing that everyone follows or does it depend on the brand.

Specifically I'm about to mount some Hope calipers but if I can't easily find them can I substitute Shimano adapters as long as I spec the correct rotor diameter? Or is the post mount spacing different such that I should run Hope adapters with Hope calipers?