Machine Design
The rolling contact bearings as compared to sliding contact bearings have

All of these
Small overall dimensions
Accuracy of shaft alignment
Low starting and low running friction except at very high speeds

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Machine Design
Jam nut is a locking device in which

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
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

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