Two important ideas in gearing are pitch surface and pitch position. The pitch surface of a gear may be the imaginary toothless surface area that you would possess by averaging out the peaks and valleys of the individual teeth. The pitch surface area of an beval gear china ordinary 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.
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 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 surfaces are at the point of intersection of the shaft axes.
Bevel gears that have pitch angles in excess of ninety degrees possess teeth that time inward and are called internal bevel gears.
Bevel gears which have pitch angles of specifically 90 degrees possess teeth that point outward parallel with the axis and resemble the points on a crown. That’s why this kind of bevel gear is named a crown gear.
Mitre gears are mating bevel gears with equal numbers of teeth and with axes at right angles.
Skew bevel gears are those that the corresponding crown gear has tooth that are directly and oblique.