IRWIN 1882789 Countersink Replacement Countersink Bit, Widened Flute, 1/4 in Dia Shank                  Tapered drill with widened flutes for drilling fast, clean pilot holes. 1/4 in quick change shank reduces slipping in standard chucks and is compatible with all 1/4 in quick change chucks, including impact drills. Adjustable four-cutter counterbore cuts and clears chips quicker for fast, smooth countersinking. Counter bore attaches to flats on shank with two hex screws for a secure fit and can be adjusted for controlled pilot hole depth.