Machine Design
Castle nut is a locking device in which

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 pin spitted and bent in reverse direction at other end
One smaller nut is tightened over main nut and main nut tightened against smaller one by loosening, creating friction jamming
A slot is cut partly is middle of nut and then slot reduced by tightening a screw

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Machine Design
Coaxing is the procedure of increasing

Metal resistance to corrosion by coating
Metal strength by cycling
Metal hardness by surface treatment
Fatigue limit by over-stressing the metal by successively increasing loadings

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