An imaginary line (often a circle) passing through the teeth of one cogwheel, pinion, rack, etc., so as to touch the corresponding line in another, without sliding, when the two components are geared together.
Origin
Late 18th century; earliest use found in John Imison (d. 1788), clockmaker and printer.
Definition of pitch line in US English:
pitch line
noun
Mechanics
An imaginary line (often a circle) passing through the teeth of one cogwheel, pinion, rack, etc., so as to touch the corresponding line in another, without sliding, when the two components are geared together.
Origin
Late 18th century; earliest use found in John Imison (d. 1788), clockmaker and printer.