Theory of Machine
The example of rolling pair is

Lead screw of a lathe
Ball bearing and roller bearing
Ball and socket joint
Bolt and nut

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Theory of Machine
The contact ratio is given by

(Length of the arc of approach)/cosφ
(Length of the path of approach)/(Circular pitch)
(Length of path of recess)/(Circular pitch)
(Length of the arc of contact)/(Circular pitch)

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Theory of Machine
In a steam engine, the earlier cut-off with a simple slide valve may be obtained by increasing the steam lap and the angle of advance of the eccentric but keeping constant the travel and lead of the valve, this method will

Reduce length of effective stroke of piston
Reduce maximum opening of port to steam
All of the listed here
Cause withdrawing or throttling of steam

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