includes Six aircraft quality precision twist drill bits in the following diameters: #40 short; #30 short; #21 short; #20 short; #13 Short & #10 short. All drill bits are black oxided to prevent chip-to-tool welding and corrosion while enhancing appearance. The drill bits comply with National Aerospace Standards. The 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 M7 tool steel with self-centering-to reduce walking, 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 threads, and are made in America. The drill bits are concentric, self-tightening, non-slipping, long life tools designed for work in limited space situations. The drill bits work in metal, wood or plastic.