In the structural design and series design of various coupling forms, the maximum and minimum range of shaft holes and the length of shaft holes are determined according to the magnitude of transmission torque, the structure of coupling and the contour strength. Each specification should be only one length of shaft holes. In foreign countries, no matter which country, almost all the enterprises that produce coupling have only one shaft hole length for each size of coupling in different standards. Due to the misleading of GB/T 3852, every shaft hole in the standard of coupling products in our country corresponds to the length of various shaft holes. It seems that only in this way can the transformation be completed when the standard of foreign coupling is converted into the standard of coupling in our country, and a variety of shaft hole lengths are added. Understanding the axle extension criterion is the main reason for this phenomenon. The axle hole of the coupling should conform to the axle extension criterion, and the length of the axle hole depends on the strength of the transmission torque hub. This kind of selection is inconvenient to choose, especially not suitable for professional production, which makes the manufacturer unable to prepare materials. Only after determining the length of the shaft hole, can the material be fed, prolonging the production cycle. In order to be in line with international standards, China is changing this unreasonable situation and keeping in line with international conventions. At present, the product standard of coupling, which is imported by National Machinery Shaft and Annex Standards Committee, has been revised to achieve only one shaft hole length per specification. The revised standards are: JB/T 8869 serpentine spring coupling, JB/T 9147 diaphragm coupling and JB/T9148 elastic block coupling.
Shafting transmission usually consists of one or more coupling connecting the main and driven shafts to form a shafting transmission system to transfer torque and motion. The coupling is mainly connected with the shaft of motor, reducer and worker. The form, connection form and size of the shaft hole mainly depend on the form and size of the coupling. The cylindrical or conical axle extension international standard design shaft is generally installed in product design. The axle extension standard is designed for the axle.