Coupling is a component used to connect a drive shaft and a driven part, for example, a motor shaft and a ball screw for the purpose of transmitting the torque.
The main roles of a coupling include the following:

• Connecting drive shafts of motors, etc. with driven shafts of ball screws etc. to transmit power.
• Providing tolerance for errors (misalignment) between the cores of the drive shaft and the driven shaft.
• Absorbing equipment impacts and vibration.
• Improving equipment performance.

Also, Coupling introduces mechanical flexibility providing misalignment for the shafts. As a result, this coupling flexibility can prevent uneven wear, vibration, and other mechanical troubles due to misalignment.