Skew bevel gears are those for which the corresponding crown equipment has teeth that are directly and oblique.
Mitre gears are mating bevel gears with equal numbers of teeth and with axes at right angles.
Bevel gears that have pitch angles of exactly 90 degrees have teeth that point outward parallel with the axis and resemble the points on a crown. That’s why this type of bevel gear is named a crown gear.
Bevel gears which have pitch angles in excess of ninety degrees possess teeth that point inward and are called internal bevel gears.
The most familiar types of bevel gears have pitch angles of less than 90 degrees and therefore are cone-shaped. This type of bevel gear is called external because the gear teeth stage outward. The pitch surfaces of meshed external bevel gears are coaxial with the gear shafts; the apexes of both areas are at the point of intersection of the shaft axes.
Two important principles in gearing are pitch surface area 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 individual teeth. The pitch surface of an ordinary gear is the form of a cylinder. The pitch angle of a equipment is the angle between your encounter of the pitch surface and the axis.