In article ,
says...
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.

I have seen 60, 82 and 100 degrees but never 90.

Most metric flat heads are 90 degrees.

Ned Simmons