Two important ideas in gearing are pitch surface area and pitch position. 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 beval gearbox ordinary gear is the shape of a cylinder. The pitch angle of a gear is the angle between your encounter of the pitch surface and the axis.
The most familiar kinds of bevel gears have pitch angles of significantly less than 90 degrees and they are cone-shaped. This kind of bevel gear is named external because the gear teeth stage outward. The pitch areas of meshed exterior bevel gears are coaxial with the apparatus shafts; the apexes of the two surfaces are at the idea of intersection of the shaft axes.
Bevel gears which have pitch angles of greater than ninety degrees possess teeth that time inward and are called internal bevel gears.
Bevel gears which have pitch angles of precisely 90 degrees possess teeth that time outward parallel with the axis and resemble the factors 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 numbers of teeth and with axes at right angles.
Skew bevel gears are those for which the corresponding crown equipment has the teeth that are directly and oblique.