This is the simplest form of bevel gear. Unusually the drive was by shaft and bevel gear. It had a single-speed shaft drive turned by a bevel gear. This meshes with another bevel gear mounted on the drive shaft. That's why this type of bevel gear is called a crown gear. This type of bevel gear is called external because the gear teeth point outward. The differential is a Salisbury 4HU or Dana unit with a hypoid spiral bevel gear. In a bevel gear it is the diameter of the crown circle. Furthermore, the "involute bevel gear sets" cause more noise. Furthermore, those "involute bevel gear sets" cause more noise. Addendum angle in a bevel gear, is the angle between face cone and pitch cone. For a bevel gear, different definitions for effective face width are applicable. A spiral bevel gear is a bevel gear with helical teeth. Each axle was driven by a separate bevel gear, with no side rods. A pitch cone of any other angle is simply called a bevel gear.