Two important concepts in gearing are pitch planetary gearbox surface and pitch position. The pitch surface area 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 area 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 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 gear shafts; the 
apexes of both areas 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 so are called internal bevel gears.
Bevel gears that have pitch angles of exactly 90 degrees possess 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 the same amounts of teeth and with axes at right angles.
Skew bevel gears are those that the corresponding crown equipment has teeth that are straight and oblique.