A coupling is a device used to connect two shafts together on a semi-permanent nature at their ends for the purpose of transmitting power. The primary purpose of couplings is to join two pieces of rotating equipment while permitting some degree of misalignment or end movement or both.

Couplings is useful to joining manageable length drive shafts to form long drive shafts such as in ship propeller shafts.

Couplings can be removed for maintenance purposes between drives and machines. 

Couplings can be classified in the following: Video

• Fixed (fast) (permanent) (rigid) couplings
• Flexible couplings
• Self alignment couplings
• Fluid couplings Note: Can also be classified as a clutch https: Video