Worm and Worm Gear:

Worm and worm gear are utilized to connect two skew shafts at right angle to each other. Worm may be single, double or triple start. Worm and worm gear are illustrated in given figure. Some of the special terminology utilized with worm and worm gear is as:

Axial Pitch (Px)

This is the distance among corresponding points on adjacent teeth of worm measured along with direction of the axis.

Lead

The distance by which a helix advances along with the helix of the gear for one turnaround is called lead.