Two important principles in gearing are pitch surface area and pitch angle. The pitch surface of a gear may be the imaginary toothless surface that you would have got by averaging out the peaks and valleys of the average person teeth. The pitch surface of a typical gear is the form of a cylinder. The pitch angle of a gear 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 less than 90 degrees and they are cone-shaped. This type of bevel gear is named external because the gear teeth point outward. The pitch areas of meshed external bevel gears are coaxial with the apparatus shafts; the apexes of the two surfaces 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 so are called internal bevel gears.
Bevel gears that have pitch angles of beval gear china specifically 90 degrees have teeth that time outward parallel with the axis and resemble the points on a crown. That is why this kind of bevel gear is named a crown gear.
Mitre gears are mating bevel gears with 
the same numbers of teeth and with axes at right angles.
Skew bevel gears are those for which the corresponding crown gear has tooth that are directly and oblique.