Workpiece materials:Aluminum and brass are typical workpieces with good to excellent machinability ratings. Cast iron, mild steel and plastic have good ratings. 8..Tapered drill with widened flutes for drilling fast, clean pilot holes and ensures tight fit for screws 9.Adjustable four-cutter counter bore cuts and clears chips quicker for fast, smooth countersinking 10..Counter bore attaches to flats on shank with two hex screws for a secure fit and can be adjusted for controlled pilot hole depth 11..1/4" quick-change shank reduces slipping in standard chucks and is compatible with all 1/4" quick-change chucks, including impact drills 12.Adjustable stop collar attaches to counter bore with two hex screws for a secure fit and can be adjusted for desired counter bore depth.