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2 Countersink Depth

The following diagram shows how the countersink depth is determined.


For any given countersink angle, the depth of a perfect countersink recess is a constant fraction of the screw head diameter. The following table shows the fractions for each of the countersink angles listed by Severance Tools . I’ve never needed any but the 82 and 90 but you never know so I calculated them all. The derivation math is at the end of this article.


So, if you have, say, an 82° 10-32 FHMS whose head diameter measures .366”, then its countersink depth will be .366 {\times} .575 = .210{in}. In my experience, the heads of mass-market fasteners don’t seem to be made to any particular standard, are pretty variable in diameter and really need to be measured. It must give the CNC folks real headaches.