Pitch line , ∨ Pitch circle Meaning, Definition & Usage

Definitions
  1. (Gearing), an ideal line, in a toothed gear or rack, bearing such a relation to a corresponding line in another gear, with which the former works, that the two lines will have a common velocity as in rolling contact; it usually cuts the teeth at about the middle of their height, and, in a circular gear, is a circle concentric with the axis of the gear; the line, or circle, on which the pitch of teeth is measured.

Webster 1913