This set pilot drills and countersinks at the same time, producing a faster finish. Heavy-duty design manufactured from carbon steel C45. Replaceable drill bits manufactured from high-speed steel. Drill bits can be adjusted and fastened with a hex set screw. For countersinking screw holes for flush fitting of screwheads in hardwood, soft wood and plastics. Fitted with quick change 1/4" hex. shank. Compatible with drills with a standard 10/13mm chuck.