Theory of Machine
When the nature of contact between the elements of a pair is such that one element can turn about the other by screw threads, the pair is known as a

Screw pair
Turning pair
Sliding pair
Spherical pair

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Theory of Machine
Higher pairs are those which have

Surface contact between the two elements when in motion
Point or line contact between the two elements when in motion
Elements of pairs not held together mechanically
Two elements that permit relative motion

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