Because the tooth profile curve of a gear is determined by the size of its base circle, which is also related to the modulus, number of teeth, and tooth shape angle of the gear. Therefore, gears with the same modulus and tooth shape angle but different tooth numbers should have different milling cutters, which requires manufacturing many milling cutters with different tooth shapes, which is very uneconomical. Therefore, for gear disc milling cutters with the same modulus and tooth shape angle, they are segmented and numbered according to the number of teeth of the processed gear. For gears with the same number of teeth in the segment, the tooth shape error generated by the same gear milling cutter is allowed for gears with low accuracy requirements. This is more economical and feasible, so the gear disc milling cutter needs to be semicoloned.

There are two segmentation numbering methods for standard gear disc milling cutters, with 8 pieces per set when m=1-8mm. 1 to 8 respectively; When m=9-16mm, each set consists of 15 pieces, including No. 1, No. 1.5, No. 2, No. 2.5,... No. 8.