Two important principles in gearing are pitch surface area and pitch angle. The pitch surface of a gear may be the imaginary beval gear china toothless surface that you would have by averaging out the peaks and valleys of the average person teeth. The pitch surface area of an ordinary gear is the shape of a cylinder. The pitch angle of a gear is the angle between the encounter of the pitch surface area and the axis.

The most familiar kinds of bevel gears have pitch angles of significantly less than 90 degrees and therefore are cone-shaped. This kind of bevel gear is called external because the gear teeth stage outward. The pitch surfaces of meshed external bevel gears are coaxial with the gear shafts; the apexes of both areas are at the idea of intersection of the shaft axes.

Bevel gears which have pitch angles in excess of ninety degrees have teeth that time inward and are called internal bevel gears.

Bevel gears that have pitch angles of precisely 90 degrees possess teeth that time outward parallel with the axis and resemble the points on a crown. That is why this type of bevel gear is named a crown gear.

Mitre gears are mating bevel gears with equal amounts of teeth and with axes in right angles.

Skew bevel gears are those for which the corresponding crown gear has teeth that are directly and oblique.