Editing Gear (section)

==Standard pitches and the module system==<!-- [[Module (gears)]] redirects here -->
Although gears can be made with any pitch, for convenience and interchangeability standard pitches are frequently used. Pitch is a property associated with linear [[dimension]]s and so differs whether the standard values are in the [[Imperial units|imperial]] (inch) or [[metric system|metric]] systems. Using ''inch'' measurements, standard diametral pitch values with units of "per inch" are chosen; the ''diametral pitch'' is the number of teeth on a gear of one inch pitch diameter. Common standard values for spur gears are 3, 4, 5, 6, 8, 10, 12, 16, 20, 24, 32, 48, 64, 72, 80, 96, 100, 120, and 200.<ref name="Berg">{{cite web |url=http://www.wmberg.com/catalog/pdf/b00k2-16.pdf |title=W. M. Berg Gear Reference Guide |url-status=dead |archive-url=https://web.archive.org/web/20150421051810/http://www.wmberg.com/catalog/pdf/b00k2-16.pdf |archive-date=21 April 2015 }}</ref> Certain standard pitches such as ''{{frac|1|10}}'' and ''{{frac|1|20}}'' in inch measurements, which mesh with linear rack, are actually (linear) ''circular pitch'' values with units of "inches"<ref name=Berg/>

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 millimetres 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. Module is a direct dimension ("millimeters per tooth"), unlike diametral pitch, which is an inverse dimension ("teeth per inch"). Thus, if the pitch diameter of a gear is 40&nbsp;mm and the number of teeth 20, the module is 2, which means that there are 2&nbsp;mm of pitch diameter for each tooth.<ref name="MH26">{{Citation |title= Machinery's Handbook |last1=Oberg |first1= E. |last2=Jones |first2=F. D. |last3=Horton |first3=H. L. |last4=Ryffell |first4=H. H. |year=2000 |edition=26th |publisher=Industrial Press |isbn=978-0-8311-2666-7 |page=2649 |postscript=.}}</ref> The preferred standard module values are 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.8, 1.0, 1.25, 1.5, 2.0, 2.5, 3, 4, 5, 6, 8, 10, 12, 16, 20, 25, 32, 40 and 50.<ref>{{cite web |url=http://qtcgears.com/tools/catalogs/PDF_Q420/Tech.pdf| title=Elements of metric gear technology}}</ref>