Two important concepts in gearing are pitch surface area and pitch position. The pitch surface of a gear is the imaginary toothless surface that you would have got by averaging out the peaks and valleys of the individual teeth. The pitch surface area of a typical gear is the shape of a cylinder. The pitch angle of a gear is the angle between the face of the pitch surface and the axis.
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 named external since the gear teeth stage outward. The pitch surfaces of meshed exterior bevel gears are coaxial with the apparatus shafts; the apexes of both areas are at the point of intersection of the shaft axes.
Bevel gears that have pitch angles in excess of ninety degrees beval gear china possess teeth that time inward and are called internal bevel gears.
Bevel gears that have pitch angles of specifically 90 degrees possess teeth that point outward parallel with the axis and resemble the factors on a crown. That is why this type of bevel gear is named a crown gear.
Mitre gears are mating bevel gears 
with the same amounts of teeth and with axes in right angles.
Skew bevel gears are those that the corresponding crown equipment has teeth that are straight and oblique.