Combination Drill/Tap Bits. 1/4-20NC. Complete hole drilling, tapping and deburring/countersinking in one operation with power drill saves labor and time. Back tapered beyond tap to prevent thread damage from over-drilling. Deburr/countersink also provided on bit beyond back taper. Made from hardened high-speed steel vs. carbon steel for longer life. High quality hex shank to ensure strong connection to drill chuck. Designed to tap up to 10-gauge metal. Quick change adaptor included in both metric and standard kits.