Worm 1 rotates about fixed axis A and meshes with worm wheel 3 which is keyed to shaft 5 and rotates about fixed axis B-B. Also keyed to shaft 5 is worm wheel 4 which meshes with worm 2. Worm 2 rotates about fixed axis C. The transmission ratio of the mechanism is i₁₂=(z₃/z₁)(z₂/z₄) where z₃ and z₄ are the numbers of teeth on wheels 3 and 4, and z₁ and z₂ are the numbers of threads (starts) on worms 1 and 2. If worm 1 is the driving link, worm 2 will rotate only if its lead angle exceeds the angle of friction. Since the efficiency in a transmission from worm wheel to worm is very low (less than 0.5), this reducing gear cannot be employed for power drives, but it may prove expedient for low-power high-ratio drives.
$2829$WG,SR$