Rack jacks, also called the rack lifting (Rack-Pinion jack). Rack as a rigid top piece jack. Rack jack rack, gear, handle. Levers and gear driven by the human the rack top heavy lifting. Weight is generally not more than 20 tons, and long-term support heavy loads, or need to use the lower part of the claws to enhance the occasion of the weight is mainly used in the operating conditions inconvenient places, such as railway from the rail operations.