Speed reducer selection needs to understand the parameter requirements
1) what equipment is the reducer used for to determine the safety factor of SF (SF = rated power of reducer/motor). Installation method (rectangular shaft, parallel shaft, output hollow shaft key, output hollow shaft lock plate, etc.), etc
2) motor power, motor series (4P, 6P or 8P of the motor)
3) the ambient temperature around the reducer (decide to check the thermal power of the reducer)
4) radial force and axial force of output shaft of reducer. To provide axial and radial forces, it is best to find a sample and refer to it.
5) specific parameters of reducer (speed ratio, accuracy, torque, etc.)