Two important principles in gearing are pitch surface and pitch position. The pitch surface area of a gear may be the imaginary toothless surface area that you would possess by averaging out the peaks and valleys of the average person teeth. The pitch surface of an ordinary gear is the shape of a cylinder. The pitch angle of a gear is the angle between the face of the pitch surface area and the axis.
The most familiar types of bevel gears have pitch angles of significantly less than 90 beval gear china degrees and they are cone-shaped. This type of bevel gear is called external because the gear teeth stage 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 which have pitch angles of greater than ninety degrees possess teeth that point inward and are called internal bevel gears.
Bevel gears which have pitch angles of specifically 90 degrees have teeth that time outward parallel with the axis and resemble the points on a crown. That is 
why this type of bevel gear is called a crown gear.
Mitre gears are mating bevel gears with equivalent numbers of teeth and with axes in right angles.
Skew bevel gears are those that the corresponding crown equipment has tooth that are straight and oblique.