IRWIN 1882783 Countersink Drill Bit, 2-5/16 in L 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.