Irwin Tools 1877720  Countersink Drill Bit,  Black Oxide, 3-Piece Precision-ground 82 tip for countersinking into most machinable metals, wood or plastic Made from industrial grade high speed steel for increased durability Includes a black oxide finish for added corrosion resistance Five flute design reduces vibration for smoother drilling and extended life 1/4" round shank fits all handheld and stationary drills