Skew bevel gears are those for which the corresponding crown gear has teeth that are straight and oblique.
Mitre gears are mating bevel gears with equivalent amounts of teeth and with axes in right angles.
Bevel gears that have pitch angles of precisely 90 degrees possess teeth that point outward parallel with the axis and resemble the points on a crown. That is why this type of bevel gear is called 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 kinds of bevel gears have pitch angles of significantly less than 90 degrees and therefore are cone-shaped. This kind of bevel gear is named external since the gear teeth point outward. The pitch areas of meshed external bevel gears are coaxial with the gear shafts; the apexes of the two surfaces are at the point of intersection of the shaft axes.
Two important principles in gearing are pitch surface area and pitch angle. The pitch surface 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 of a typical gear is the shape of a cylinder. The pitch angle of a equipment is the angle between your face of the pitch surface and the axis.