Machine Design
The maximum efficiency of a square threaded screw is

(1 + sinφ)/ (1 - sinφ)
(1 - sinφ)/ (1 + cosφ)
(1 + cosφ)/ (1 - sinφ)
(1 - sinφ)/ (1 + sinφ)

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Machine Design
A tap bolt

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

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