Two important concepts in gearing are pitch surface area and pitch angle. The pitch surface of a gear is the imaginary toothless surface that you would have by averaging out the peaks and valleys of the individual 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 beval gearbox 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 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 which have pitch angles of greater than ninety degrees have teeth that time inward and so are called internal bevel gears.
Bevel gears that have pitch angles of specifically 90 degrees have teeth that time outward parallel with the axis and resemble the points on a crown. That is why this kind of bevel gear is called a crown gear.
Mitre gears are mating bevel gears with equal amounts of teeth and with axes at right angles.
Skew bevel gears are those for which the corresponding crown equipment has teeth that are straight and oblique.