Machine Design
A screw will be self locking, if

Friction angle is equal to helix angle
Friction angle is less than helix angle
Efficiency of screw is 100%
Friction angle is more than helix angle

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Machine Design
A stud

Has head at one end and other end fits into a tapped hole in the other part to be joined
Has pointed threads
Has both the ends threaded
Has a head on one end and a nut fitted to the other

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

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