Two important ideas in gearing are pitch surface area and pitch position. The pitch surface of a gear may be the imaginary toothless surface that you would have by averaging out the peaks and valleys of the average person teeth. The pitch surface area of a typical gear is the form of a cylinder. The pitch angle of a equipment is the angle between the encounter of the pitch surface and the axis.
The most familiar types of bevel gears have pitch 
angles of less than 90 planetary gearbox degrees and they are cone-shaped. This type 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 both surfaces are at the point of intersection of the shaft axes.
Bevel gears which have pitch angles in excess of ninety degrees possess teeth that time inward and are called internal bevel gears.
Bevel gears that have pitch angles of specifically 90 degrees possess teeth that time outward parallel with the axis and resemble the factors 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 amounts of teeth and with axes in right angles.
Skew bevel gears are those that the corresponding crown equipment has teeth that are straight and oblique.