Two important concepts in gearing are pitch surface and pitch angle. The pitch surface area of a gear is the imaginary toothless surface that you would have got by beval gearbox averaging out the peaks and valleys of the average person teeth. The pitch surface of a typical gear is the form of a cylinder. The pitch angle 
of a gear is the angle between your face of the pitch surface area and the axis.
The most familiar kinds 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 point outward. The pitch areas of meshed external bevel gears are coaxial with the apparatus shafts; the apexes of both areas are at the idea of intersection of the shaft axes.
Bevel gears that have pitch angles of greater than ninety degrees possess teeth that time inward and so are called internal bevel gears.
Bevel gears that have pitch angles of specifically 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 equivalent amounts of teeth and with axes at right angles.
Skew bevel gears are those for which the corresponding crown gear has tooth that are straight and oblique.