Irwin Tools 1890451 Countersink Wood Drill Bit Set, 19-Piece Tapered drill with widened flutes for drilling fast, clean pilot holes and ensures tight fit for screws Adjustable four-cutter counter bore 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 1/4" quick-change shank reduces slipping in standard chucks and is compatible with all 1/4" quick-change chucks, including impact drills Adjustable stop collar attaches to counter bore with two hex screws for a secure fit and can be adjusted for desired counter bore depth