Two important concepts in gearing are pitch surface area and pitch angle. The pitch surface of a gear is the imaginary toothless surface area that you would have got by averaging out the peaks and valleys of the beval gearbox 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 your face of the pitch surface and the axis.
The most familiar kinds of bevel gears have pitch angles of less than 90 degrees and therefore are cone-shaped. This kind of bevel gear is named external because the gear teeth point outward. The pitch surfaces of meshed exterior bevel gears are coaxial with the gear shafts; the apexes of both surfaces are at the idea of intersection of the shaft axes.
Bevel gears that have pitch angles of greater than ninety degrees possess teeth that time inward and so are called internal bevel gears.
Bevel gears that 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 type of bevel gear is called 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 oblique.