sentences:  Certain standard pitches such as "1/10" and "1/20" in inch measurements, which mesh with linear rack, are actually (linear) "circular pitch" values with units of "inches"
  
  When gear dimensions are in the metric system the pitch specification is generally in terms of module or "modulus", which is effectively a length measurement across the "pitch diameter".The term module is understood to mean the pitch diameter in millimeters divided by the number of teeth.When the module is based upon inch measurements, it is known as the "English module" to avoid confusion with the metric module.