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. 100 degrees seems to
be very common on rivets intended for sheet metal. Most machine and
wood screws I've seen are 82 degrees.

Also I have a couple of countersink tools from Boeing Surplus that takes
a removable piloted bit and has a micrometer depth adjustment. I set it
up on a piece of scrap and then countersink as many holes as I need very
quickly. I could post a picture if it would help. Wonderfull gadget!
Even gives me accurate countersinks when used in a hand held electric
drill.

Ted