Machine Design
Castle nut is a locking device in which

A slot is cut partly is middle of nut and then slot reduced by tightening a screw
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
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
One smaller nut is tightened over main nut and main nut tightened against smaller one by loosening, creating friction jamming

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Machine Design
Which of the following statement is correct regarding power screws?

If the friction angle is less than the helix angle of the screw, then the efficiency will be more than 50%
Both (A) and (B)
The efficiency of a self locking screw can not be more than 50%
The efficiency of Acme (trapezoidal) thread is less than that of a square thread

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