the recirculating ball steering mechanism contains a worm gear inside a block with a threaded hole in it; this block has gear teeth cut into the outside to engage the sector shaft (also called a sector gear) which moves the pitman arm. the steering wheel connects to a shaft, which rotates the worm gear inside of the block. instead of twisting further into the block, the worm gear is fixed so that when it rotates, it moves the block, which transmits the motion through the gear to the pitman arm, causing the roadwheels to turn.