Editing Involute gear (section)

==Line of action and contact==
The point where the line of action crosses the line between the two centres is called the [[gear#Pitch|pitch point]] of the gears. The sliding contact friction is zero at this point.

The distance actually covered on the line of action is then called ''line of contact''. The line of contact begins at the intersection between the line of action and the addendum circle of the driven gear and ends at the intersection between the line of action and the addendum circle of the driving gear.<ref>{{Cite web|url=https://www.tec-science.com/mechanical-power-transmission/involute-gear/meshing-line-action-contact-pitch-circle-law/|title=Meshing of involute gears|last=tec-science|date=2018-10-31|website=tec-science|language=en-US|access-date=2019-10-22}}</ref>

The [[Angle of pressure|pressure angle]] is the acute angle between the line of action and a normal to the line connecting the gear centers. The pressure angle of the gear varies according to the position on the involute shape, but pairs of gears must have the same pressure angle in order for the teeth to mesh properly, so specific portions of the involute must be matched.