Usually, tolerancing is supposed to reproduce the use of the part. how to reproduce the conical effect of the thread without tightening the nut? how to check the face once tighten?
I feel like it's a case of theorically correct drawing that is near impossible to check. Maybe by screwing this on a shaft that is very slighly bigger that the nominal thread diameter and check for runout?
I find that sometime rethinking the design is better. if perpendicularity with the surface an issue, why not use a softer material washer for example? I am not saying it's the right solution but sometime trying to fit a square in a round hole is not a good sign.
gee