Double Reduction Worm Gear Units are constructed using two single reduction worm gear units. The primary worm gear unit is specially designed to mount integrally on a standard single worm gear unit which forms the secondary stage. The complete gear unit becomes compact and rigid in arrangement for slow moving machinery. A wide range of ratio from 75:1 to 4900:1 is available. These gear units are particularly suitable for high torque slow-speed drives. Worm gearing conforms to BS-721.