Machine Design
A locking device in which the bottom cylindrical portion is recessed to receive the tip of the locking set screw, is called

Ring nut
Castle nut
Sawn nut
Jam nut

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

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