1. Hinge pair: the main rotating pair that connects the planar connecting rod into a diamond structure. The hinge is perpendicular to the axis with a slight gap, so it has high flexibility and self-adjustment ability.

2. Sliding pair: sprocket and chain rib usually used in diamond mechanism. The sliding pair has small friction and low noise, but it is easy to be damaged.

3. Rolling pair: a rotating pair that rotates by rolling or spherical contact, usually used in high-load or high-precision pan-rhombic mechanisms. Rolling pair has high wear resistance and life, but it requires high precision control.

4. Sleeve pair: A hinged rotary pair is provided in the sliding or rotating direction, which is usually used in a low-load pan-rhombic mechanism. The sleeve pair is easy to manufacture and assemble, but its rigidity and accuracy are poor when bending.