Machine Design
The maximum efficiency of a square threaded screw is

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

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Machine Design
Spring stiffness is

Ratio of coil diameter to wire diameter
Its capability of storing energy
Its ability to absorb shocks
Load required to produce unit deflection

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Machine Design
A fast and loose pulley drive is used when

Shafts are arranged parallel and rotate in the opposite directions
Driven shaft is to be started or stopped whenever desired without interfering with the driving shaft
Shafts are arranged at right angles and rotate in one definite direction
Shafts are arranged parallel and rotate in the same directions

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