Steering is worm and worm wheel type. Steering gear is by worm and worm wheel. The two elements are also called the worm screw and worm wheel. The leadscrew engaged with a worm wheel instead of the usual halfnuts. The second are single-throated worm gears, in which the worm wheel is throated. A worm is meshed with a "worm wheel", which looks similar to a spur gear.