Machine Design
The fatigue stress concentration factor is defined as

The ratio of endurance limit without stress concentration to the endurance limit with stress concentration
The product of the endurance limits with and without stress concentration
All of these
The ratio of endurance limit with stress concentration to the endurance limit without stress concentration

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Machine Design
Jam nut is a locking device in which

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
A slot is cut partly in middle of nut and then slot reduced by tightening a screw

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