Threaded TightFit® drill bits are made of M7 high-speed steel, for drilling hard, tough materials. * With a 135 degree split-point, 1/4-28 threaded shank and a 5/16" hex adapter for easy removal. * Three lengths of drill bits: LONGS=2 3/8";SHORTS=1 1/2"; and STUBS=3/4-7/8". * TightFit® drill bits are black oxided to prevent corrosion while enhancing appearance. * These drill bits comply with National Aerospace Standard NAS965.