Axial force or thrust on the worm,

Lead angle is the angle between the tangent to the thread helix on the pitch cylinder and the plane normal to the axis of the worm. It is denoted by λ.

(TE)/T = 1/cos θ.

The term normal pitch is used for a worm having single start threads. In case of a worm having multiple start threads, the term normal lead (lN) is used, such that

For number of starts from 36 and above we have single velocity ratio. For 12 to 36 we have double velocity ratio, for 8 to 12, we have triple velocity ratio and for 6 to 12 we have quadruple velocity ratio.

Face angle is the angle subtended by the face of the tooth at the cone centre. It is denoted by ‘φ’. The face angle is equal to the pitch angle plus addendum angle.

The worm gears are widely used for transmitting power at high velocity ratios between non-intersecting shafts that are generally, but not necessarily, at right angles.

Root angle is the angle subtended by the root of the tooth at the cone centre. It is denoted by ‘θR’. It is equal to the pitch angle minus dedendum angle.

When equal bevel gears (having equal teeth and equal pitch angles) connect two shafts whose axes intersect at right angle, then they are known as mitre gears.

Bevel factor = 1 – b / L.