Big Horn 18937 Set of 3 Countersinks with Matching Quick Change HSS Taper Point Drills are proudly made in the USA and are the best tools on the market today to pre-drill the head shank and threads of screws. This set includes 3/8-Inch cutting diameters in the most popular sizes #6, #8, and #10. The countersink, designed to cut clean and hardened for long wear, is held in place with 2 hex-socket screws that should be set into the flutes of the drill. The taper point drill is made from quality high speed steel and has 1/4-Inch hex power quick change adapter for the TPS-Lock System. The hardened 3/8-Inch diameter quick change plug cutter makes smooth chamfered plugs for easy starting in predrilled holes. The plug remains in the board and can be broken out with a screwdriver or the board can be sawed to free the plug. The Fuller pre-drill/plug system makes drilling, driving and plugging easier and assures the best possible holding power and the tightest fit. W. L. Fuller # 10349003C