Unusually the final drive was by a worm gear arrangement. Final drive was by underslung worm gear. The worm in the worm gear drive may have single or multiple starts. The bowl is driven by an electric motor and worm gear from beneath. The sled can be driven by a worm gear or linear motor. In a throated worm gear it is the maximum diameter of the blank. By 1921 the company was the largest worm gear manufacturer in the world. To tilt the ladle a gearbox is used and this is typically a worm gear. The gasoline-powered engine was connected to the trans-axle via a worm gear. Early trucks had a worm gear rear-end that limited the top speed of the truck. The worm gear carries the differential gearing, which protects the vehicle against rollback. Standard worm gear ratio was 7.25&colon;1, and special gearing gave a ratio of 5.17&colon;1. The worm gear may be rotated manually, or by a motor in automated positioning systems. Worm gear configurations in which the gear cannot drive the worm are called "self-locking".