Different diameters of bolts have different influence factors on the load. First of all, the material of bolt manufacturing should be selected, and then its performance grade should be determined. At the same time, the allowable stress of bolt material (allowable stress []= s/ s) should be calculated according to the yield limit and safety coefficient of the material. The diameter of the bolt is determined according to the thread standard when the allowable stress of the bolt material meets the working load of the bolt. The formula for calculating d1 of thread path is as follows.