Addendum circle
The addendum circle coincides with the tops of the teeth and is concentric with the standard (reference) pitch circle and radially distant from it by the amount of the addendum. For external gears, the addendum circle lies on the outside cylinder while on internal gears the addendum circle lies on the internal cylinder.
References
- ANSI/AGMA 1012-G05, "Gear Nomenclature, Definition of Terms with Symbols".
Source: adapted by the editor from Wikipedia, the free encyclopedia; from the article "Addendum circle". Image Credit.