Module:

This is the ratio of the pitch circle diameter to the number of teeth. Hence, the module (m) may be expressed as following

                                                                    m = d/ T                                 . . . (8.19)

From above Equations (8.16)

 p_c  = π m                                                                           . . . (8.20)

 Addendum Circle and Addendum

This is the circle passing by the tips of addendum and gear teeth are the radial distance among pitch circle and the addendum circle.