IRWIN Metal Countersink Drill Bit Set, 5 Piece, 1877793 Precision ground 82 tip for countersinking most machinable metals, wood, and 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