"Peter H." wrote:


... it could be 82 and 90 degrees, or it could be some other number ...


Countersinks are made in 60, 82 and 90 degrees.

Machine screws are 82 degrees.

Specialty screws could be 90 degrees.

Aircraft machine screws that I work with are generally 100 degrees
heads, as are the countersunk rivets. There are 120 degree heads out
there too.

Cheers
Trevor Jones