Two important concepts in gearing are pitch surface and pitch position. The pitch surface of a gear may be the imaginary toothless surface area that you would possess by averaging out the peaks and valleys of the individual teeth. The pitch surface area of a typical gear is the form of a cylinder. The pitch angle of a gear is the angle between your face of the pitch surface area and the axis.

The most familiar kinds of bevel gears have pitch angles of less than 90 degrees and therefore are cone-shaped. This type of bevel gear is named external since the gear teeth point outward. The pitch surfaces of meshed external bevel gears are coaxial with the apparatus shafts; the apexes of both surfaces are at the point of intersection of the shaft axes.

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

Bevel gears which have pitch angles of exactly 90 degrees have teeth that point outward parallel with the axis and resemble the points on a crown. That is why this kind of bevel gear is named a crown gear.

Mitre gears are mating bevel gears with the same 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 planetary gearbox oblique.