Two important concepts in gearing are pitch beval gearbox surface area and pitch position. The pitch surface of a gear is the imaginary toothless surface that you would possess by averaging out the peaks and valleys of the average person teeth. The pitch surface of an ordinary gear is the shape of a cylinder. The pitch angle of a equipment is the angle between the face of the pitch surface and the axis.
The most familiar kinds of bevel gears have pitch angles of significantly less than 90 degrees and therefore are cone-shaped. This kind of bevel gear is called external since the gear teeth stage outward. The pitch surfaces of meshed external 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 point inward and are called internal bevel gears.
Bevel gears which have pitch angles of specifically 90 degrees possess teeth that time outward parallel with the axis and resemble the points on a crown. That’s why this type of bevel gear is called a crown gear.
Mitre gears are mating bevel gears with equivalent numbers of teeth and with axes in right angles.
Skew bevel gears are those for which the corresponding crown equipment has the teeth that are straight and oblique.