Machine Design
Elastic nut is a locking device in which

One small nut is tightened over main nut and main nut tightened against smaller one by loosening, creating friction jamming
A slot is cut partly in middle of nut and then slot reduced by tightening a screw
Hard fibre or nylon cotter is recessed in the nut and becomes threaded as the nut is stewed 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 pin splitted and bent in reverse direction at other end

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Machine Design
The cracks in helical springs used in railway carriages usually start on the inner side of the coil because of the fact that

It is more stretched than the outer side during the manufacturing process
It has a lower curvature than the outer side
It is subjected to a higher stress than the outer side
It is subjected to a higher cyclic loading than the outer side

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Machine Design
A fast and loose pulley drive is used when

Shafts are arranged parallel and rotate in the same directions
Driven shaft is to be started or stopped whenever desired without interfering with the driving shaft
Shafts are arranged parallel and rotate in the opposite directions
Shafts are arranged at right angles and rotate in one definite direction

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