Until now, I've used 82 deg countersinks to seat my tang screw(s). That's the angle that commercial screws come in. For the most part, this system has worked just fine, but every now and again, if the angle of the drilled hole through the wrist is off just a tad, the countersink head just fits badly. In my last build, a Hawken rifle, I used a counterbore - actually a centre drill for a lathe, and made my own screws to match. The angle is a little steeper (don't know the precise angle in degrees) but it made fitting the tang screws so much cleaner and more professional looking (thanks Jim Kibler for that!) The interesting thing about countersink and counterbores is they come by a number system of cataloguing...3, 4, 5, etc. rather than 5/16", 3/8", etc. As far as I can determine, there is no counterbore that measures 3/8" in the head size...sucks. At least this is my experience here in the Great White North.