Recirculating ball
（重定向自Worm and sector）
Recirculating ball, also known as recirculating ball and nut or worm and sector, is a steering mechanism commonly found in older automobiles, off-road vehicles, and some trucks. Most newer cars use the more economical rack and pinion steering instead, but some upmarket manufacturers (such as BMW and Mercedes-Benz) held on to the design until well into the 1990s for the durability and strength inherent in the design. A few, including Chrysler and General Motors, still use this technology in certain models including the Jeep Wrangler.