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 possess by averaging out the peaks and valleys of the individual teeth. The pitch surface area of a typical gear is the form of a cylinder. The pitch angle of a equipment is the angle between your face of the pitch surface area and the axis.
The most familiar types of bevel gears have pitch angles of significantly less than 90 degrees and they are cone-shaped. This kind of bevel gear is called external since the gear teeth point outward. The pitch beval gear china surfaces of meshed exterior bevel gears are coaxial with the apparatus shafts; the apexes of both surfaces are at the point of intersection of the shaft axes.
Bevel gears that have pitch angles of greater than ninety degrees have teeth that point 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’s 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 teeth that are directly and oblique.
