Recirculating Ball

Also known as Worm and Sector.

A steering mechanism in which the steering shaft turns a worm gear that has a spiral groove filled with ball bearings. The worm gear and ball bearings are enclosed in an assembly called the ball nut rack (or steering gear nut), which in turn has a series of gear teeth cut into the outside of it. As the ball nut rack moves up and down the worm gear, its teeth rotate a gear connected to a steering arm, which then moves the steering linkage. The ball bearings within the ball nut rack reduce the friction between the worm gear and the block.

Recirculating-ball steering is commonly found in older vehicles, but may also be found in many modern trucks and SUVs.

See also Rack and Pinion Steering.