Black spiral tap the surface after acid treatment, better performance and cutting, for effective long high-speed operation, the hole was cut on the barrier material of the tapping operation, and general hand spiral tap tap is different, common hand tap straight into the groove, while the spiral is a spiral-type tap, tap in the tapping screw, with its upward rotation of the spiral groove can be easily discharged into the hole outside the iron, so iron residue or blockage in the groove , the resulting tap broken blade crack, it can thus increase tap life and the most high-precision thread cutting, cutting speed can be accelerated over straight slot tap 30-50%. Screw tap for scope: cutting the high toughness of the material (carbon steel, alloy steel and non-ferrous metals), not suitable for cast iron chip into the crushing of the material blind hole machining.