See under pitch surface.
(in a gear or rack) an imaginary surface forming a plane (pitch plane), a cylinder (pitch cylinder), or a cone or frustrum (pitch cone) that moves tangentially to a similar surface in a meshing gear so that both surfaces travel at the same speed.
Origin of pitch surface
First recorded in 1885–90
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
an imaginary cylinder passing through, and coaxial with, the threads of a screw so that its intersection with opposite flanks of any groove is equal to half the thread pitch
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012