Adjustable 4-cutter counterbore cuts and clears chips quicker for a fast, smooth countersink or counterbore drilling. Attaches and adjusts with 2 hex screws 1/4″ Quick Change Shank reduces slipping in standard chucks and is compatible with impact drivers. Tapered drill with widen flutes for drilling fast, clean pilot holes. Adjustable stop collar attaches to counter bore for controlling countersink depth (included in sets only). Couterbore attaches to flat on shank with for a more secure fit.