1) Sliding pair- when the two elements of a pair are connected in such a way that one element can slide relative to the other. Example- the piston and cylinder, tail stock on lathe bed.
2) Turning pair- when the two elements of a pair are connected in such a way that one element can revolve about a fixed axis of another link. Example- lathe spindle supported on head stock.
3) Rolling pair- when the two elements of a pair are connected in such a way that one can roll over another fixed link. Example- ball and roller bearings.
4) Screw pair- when the two elements of a pair are connected in such a way that one element can turn about the other by screw threads. Example- nut and bolt.
5) Spherical pair- when the two elements of a pair are connected in such a way that one element can turn about the other fixed element. Example- ball socket joint.
6) Lower pair- when the two elements of a pair have surface contact when relative motion takes place and the surface of one element slides over the surface of the other element. Example- sliding, turning and screw pairs.
7) Higher pair- when the two elements of a pair have a line or point contact when relative motion takes palace and the motion between the two elements is partly turning and partly sliding. Example- toothed gearing.
