Two important principles in gearing are pitch surface and pitch position. The pitch surface area of a gear may be the imaginary toothless surface area that you would have by averaging out the peaks and valleys of the individual teeth. The pitch surface area of a typical 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 kinds of bevel gears have pitch angles of significantly less than 90 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 the two surfaces are at the point of intersection of the shaft axes.
Bevel gears that have pitch angles of greater than Motorbase ninety degrees have teeth that time inward and so are called internal bevel gears.
Bevel gears which have pitch angles of precisely 90 degrees have teeth that point outward parallel with the axis and resemble the points on a crown. That is why this kind of bevel gear is named a crown gear.
Mitre gears are mating bevel gears with equivalent amounts of teeth and with axes in right angles.
Skew bevel gears are those that the corresponding crown equipment has tooth that are directly and oblique.