1. Parallel deviation: The amount of deviation between the two axes when the two axes are connected.

2. Angle deviation: The deviation angle of the two axes when the two axes are coupled.

3. Axial deviation: The amount of displacement of the two axes in the axial direction when the two axes are coupled.

4. Torque: When a force drives a shaft to rotate, the force is multiplied by the shaft radius to be torque, torque = force × force arm.

5. Torsional stiffness: When an object is subjected to a torsional force, it will always have a torsional deformation on its circumference. The characteristic of the magnitude of this deformation is called torsional stiffness. The high torsional stiffness means that the deformation is small, and vice versa. If the torsion stiffness is small, the amount of deformation is large.