Drill bits are made of M7 high-speed steel (HSS), for drilling hard materials 135-degree split-point, 1/4-28 threads and a 5/16 inch hex adapter for removal of drill bit Three lengths of drill bits: Longs=2-3/8 inches; Shorts=1-1/4 inches; Stubs=3/4-7/8 inch Drill bits are black oxided to prevent chip-to-tool welding and corrosion Drill bits comply with National Aerospace Standard NAS965; drill bits are American made Stub Set - 00134 The Stub Series Drill Set 00134 includes five aircraft quality twist drill bits in the following drill diameters: 3/32, 1/8, 5/32, 3/16 & 1/4 inches. The overall length, not including the threads, is 1/2” - 5/8". All TightFit threaded shank drill bits are black oxided to add lubricity, prevent corrosion while enhancing appearance. The drill bits comply with National Aerospace Standards. The NAS 907B Standard provides the following description, "A special short flute, heavy duty drill designed for drilling the hard, high strength alloys used in aircraft manufacturing." The drill bits are made from M2 or M7 tool steel with self-centering, 135 degree, P3, split points and a Rockwell C scale hardness of 63.5 to 66. They are manufactured as right-hand tools with 5/16" hex wrench flats and 1/4-28 UNF-2A threads. TightFit threaded shank drill bits are concentric, self-tightening, non-slipping drills designed for work in limited space situations. They can be used to drill metal, wood, or plastic.