Suitable for processing small aperture thread and relatively high hardness of the workpiece, three buckle teeth good steel, high strength, not easy to break, gray and black coating intermediate nano laminated structure with high toughness and high compressive stress, especially suitable for processing carbon steel, 45 steel, 20Cr, S136, 40Cr, 42Cr, die steel, quenched steel and so on with Three-Thread Milling Cutters.