IRWIN Wood Countersinks feature a tapered drill and wide flutes that drill fast, clean pilot holes, and ensure a tight fit for screws. They have an adjustable four-cutter counterbore attachment that cuts fast and clears chips quickly for fast, smooth countersinking applications. The counterbore feature attaches flats on shank with two hex screws for a secure fit, and can be adjusted for controlled pilot hole depth. IRWIN SPEEDBOR countersink bits fit all standard 1/4 quick-change chucks, including impact drills.