The selection of coupling mainly considers the speed of the transmission shaft, the load, the installation accuracy of the connected two parts, the stability of rotation, the price, etc. Referring to the characteristics of various types of coupling, a combined type of coupling is selected.

Most couplings have been standardized or standardized. The designer's task is selection, not design. The basic steps of selecting coupling are as follows:

1) The magnitude and nature of the torque to be transmitted and the requirements for cushioning and vibration reduction function. For example, for high-power heavy-duty transmission, teeth coupling can be selected; for severe impact load or transmission requiring eliminating torsional vibration of shafting, tyre coupling and other coupling with high elasticity can be selected.

2) The working speed of the coupling and the centrifugal force caused by it. For high-speed transmission shafts, coupling with high balance accuracy, such as diaphragm coupling, should be selected instead of slider coupling with eccentricity.

3) The relative displacement of two axes. Flexible coupling should be selected when it is difficult to keep the two axes in precise alignment after installation and adjustment, or when the two axes will produce large additional relative displacement during operation. For example, when the radial displacement is large, slider couplings can be selected, and universal couplings can be used when the angular displacement is large or two axes intersect.

4) Reliability and working environment of coupling. Usually the non-lubricated coupling made of metal elements is more reliable; the performance of the lubricated coupling is easily affected by the degree of lubrication perfection, and may pollute the environment. Coupling with rubber and other non-metallic elements is sensitive to temperature, corrosive medium and strong light, and easy to aging.

5) Because of manufacturing, installation, load deformation and temperature change, it is difficult to keep the two axes aligned strictly and accurately after installation and adjustment. There is a certain degree of x, Y direction displacement and skewness CI. When the radial displacement is large, slider couplings can be selected, and universal couplings can be used for large angular displacement or intersecting two axes. Flexible couplings should be selected when the additional relative displacement of the two axes occurs in the working process.