Coupling refers to a device that connects two shafts or shafts and rotating parts, and rotates together in the process of transmitting motion and power, and does not disengage under normal circumstances. Sometimes it is also used as a safety device to prevent the connected parts from being subjected to excessive loads, and plays the role of overload protection. Couplings can be divided into two categories: rigid couplings and flexible couplings.

Rigid couplings do not have cushioning and the ability to compensate for the relative displacement of the two axes. The two shafts are required to be strictly aligned, but this type of coupling has a simple structure, low manufacturing cost, and assembly and disassembly. 2. Convenient maintenance, can ensure high alignment of the two shafts, large transmission torque and wide application. Commonly used are flange coupling, sleeve coupling and clamp coupling.

Flexible couplings can be divided into flexible couplings without elastic elements and flexible couplings with elastic elements. The former type only has the ability to compensate for the relative displacement of the two axes, but it cannot buffer the vibration. Block couplings, toothed couplings, universal couplings and chain couplings, etc.; the latter category contains elastic elements, in addition to the ability to compensate for the relative displacement of the two axes, it also has buffering and vibration reduction effects. However, due to the limitation of the strength of the elastic element, the transmitted torque is generally not as good as the flexible coupling without the elastic element. The common ones are the elastic sleeve pin coupling, the elastic pin coupling, the plum blossom coupling, and the tire type. Couplings, serpentine spring couplings, reed couplings, etc.