Machine Design
The function of the washer is to

Provide bearing area
Absorb shocks and vibrations
Fill up the axial gap
Provide cushioning effect

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Machine Design
Jam nut is a locking device in which

Through slots are made at top and a cotter pin is passed through these and a hole in the bolt, and cotter spitted and bent in reverse direction at other end
A slot is cut partly in middle of nut and then slot reduced by tightening a screw
One smaller nut is tightened over main nut and main nut tightened against smaller one by loosening, creating friction jamming
A hard fibre or nylon cotter is recessed in the nut and becomes threaded as the nut is screwed on the bolt causing a tight grip

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