<P> The pitch helix is the intersection of the tooth surface and the pitch cylinder of a helical gear or cylindrical worm . </P> <P> The base helix of a helical, involute gear or involute worm lies on its base cylinder . </P> <P> Base helix angle is the helix angle on the base cylinder of involute helical teeth or threads . </P> <P> Base lead angle is the lead angle on the base cylinder . It is the complement of the base helix angle . </P>

The part of the tooth between the pitch circle and dedendum circle is called