Theory of Machine
The type of pair formed by two elements which are so connected that one is constrained to turn or revolve about a fixed axis of another element is known as

Rolling pair
Turning pair
Spherical pair
Sliding pair

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Theory of Machine
Higher pairs are those which have

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

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