scope:

A clear and accurate understanding of the elements involved is indispensable to all who deal with the design, dimensioning, cutting and measurement of gear teeth. The information here presented has been collected and arranged with the idea of making the important geometrical relationships as easy to see as possible with the intention of providing a sound basis for a thoroughly logical and comprehensive system of gear geometry.

The accurate exchange of ideas requires the exact definition and use of terms. Nowhere is this true to a greater degree than in the case of the present subject. Therefore, we will begin with a definition.