Two important ideas in gearing are pitch surface area and pitch position. The pitch surface area of a gear is the imaginary toothless surface that you would possess by averaging out the peaks and valleys of the individual teeth. The pitch surface area of an ordinary gear is the form 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 types of bevel gears have pitch angles of less than 90 degrees and therefore are cone-shaped. This type of bevel gear is called external because the gear teeth stage outward. The pitch areas of meshed exterior bevel gears are coaxial with the gear shafts; the apexes of both areas are at the point of intersection of the shaft axes.

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

Bevel gears which have pitch angles of exactly 90 degrees have teeth that time beval gearbox outward parallel with the axis and resemble the points on a crown. That’s why this type of bevel gear is called a crown gear.

Mitre gears are mating bevel gears with the same numbers of teeth and with axes at right angles.

Skew bevel gears are those that the corresponding crown equipment has teeth that are directly and oblique.