Crown gears or contrate gears are a particular form of bevel gear whose teeth project at right angles to the plane of the wheel; in their orientation the teeth resemble the points on a crown. A crown gear can only mesh accurately with another bevel gear, although crown gears are sometimes seen meshing with spur gears. A crown gear is also sometimes meshed with an escapement such as found in mechanical clocks.

Operating pitch diameters 

Diameters determined from the number of teeth and the center distance at which gears operate.Example for pinion:

Diametral pitch (transverse), P_d 

Ratio of the number of teeth to the standard pitch diameter in inches.

Normal diametral pitch, P_nd 

Value of diametral pitch in a normal plane of a helical gear or worm.

Angular pitch, θ_N, τ 

Angle subtended by the circular pitch, usually expressed in radians.

degrees or radians

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