Big Horn 13201 self-centering countersink bits let you drill and countersink perfect holes in one easy step – without changing or re-chucking bits. The set includes four bits for pilot holes: #6, #8, #10, and #12. Bits are adjustable (with included Allen Wrench) so you can choose your depth. Bits have a standard 1/4" hex shank for quick change with any power drill. 3/8" plug cutter bit and Allen wrench included. 3/8" Plug cutter is only for #6, #8 & #10 Bits. #12 Bit requires a 7/16" Plug cutter (not Included).