Machine Design
The efficiency of a square threaded screw is maximum if the helix angle is equal to(Where φ = Angle of friction)

45° + φ/2
45° - φ
90° - φ
45° - φ/2

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Machine Design
A stud

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

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