1. Torque T: T ↑, choose rigid coupling, non-elastic element or flexible coupling with metal elastic element; T has impact vibration, choose flexible coupling with elastic element; 

     2. Rotation speed n: n ↑, flexible coupling of non-metal elastic element; 

     3. Neutrality: Rigid coupling is better for neutrality, flexible coupling when compensation is needed; 

     4. Environment: If working at high temperature, couplings with non-metallic components are not optional; 

     5. Cost: Under the same conditions, try to choose a coupling with low price and simple maintenance.