Two important concepts in gearing are pitch surface and pitch position. The pitch surface area of a gear is the imaginary toothless surface area that you would have by averaging out the peaks and valleys of the individual teeth. The pitch surface area of a typical gear is the form of a beval gear china 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 significantly less than 90 degrees and therefore are cone-shaped. This type of bevel gear is called external since the gear teeth point outward. The pitch areas of meshed exterior 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 in excess of ninety degrees possess teeth that time 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 factors on a crown. That is why this type of bevel gear is called a crown gear.
Mitre gears are mating bevel gears with equivalent amounts of teeth and with axes in right angles.
Skew bevel gears are those that the corresponding crown gear has tooth that are straight and oblique.