Addendum

Addendum, abbreviated as A, is the radial distance between the pitch circle (a theoretical circle representing the point where the gears mesh) and the top of a gear tooth.  It is essentially the height of the tooth above the pitch circle.  The addendum is an important parameter in gear design because it affects the overall size and performance of the gear.  The addendum, along with the dedendum (the radial distance between the pitch circle and the bottom of the tooth), determines the overall tooth depth.

 

Addendum formula
\( A \;=\; 1 \;/\;DP\)     (Addendum) \( DP \;=\; 1 \;/\; A\)
Symbol	English	Metric
\( A \) = addendum	\(in\)	\(mm\)
\( DP \) = dimetrical pitch	\(in\)	\(mm\)