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
A hollow saddle key is

A taper key which fits half in the key way of hub and half in the key way of shaft
A taper key which fits in a key way of the hub and the bottom of the key is shaped to fit the curved surface of the shaft
Provided in pairs at right angles and each key is to withstand torsion in one direction only
A taper key which fits in a key way of the hub and is flat on the shaft

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Machine Design
In case of thick cylinders, the tangential stress across the thickness of cylinder is

Maximum at the outer surface and minimum at the inner surface
Maximum at the inner surface and zero at the outer surface
Maximum at the inner surface and minimum at the outer surface
Maximum at the outer surface and zero at the inner surface

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