The screw jack, also known as the mechanical jack, is driven by a manpower through a screw pair, and a screw or nut sleeve is used as a jacking member. The ordinary screw jack supports the weight by the thread self-locking function, and the structure is simple, but the transmission efficiency is low and the return stroke is slow. The thread of the self-propelled screw jack has no self-locking action and is equipped with a brake. When the brake is released, the weight can be quickly lowered by itself and the return time can be shortened, but the structure of the jack is complicated. The screw jack can support heavy objects for a long time, and the maximum lifting capacity has reached 100 tons, which is widely used. After the horizontal screw is mounted on the lower part, the weight can be traversed at a small distance.

Principle of use: Mechanical jack is one of the types of manual lifting tools. Its compact structure makes reasonable use of the swing of the rocker to make the pinion rotate. After a pair of conical gears, it can drive the screw to rotate and push the lifting sleeve. The object rises or falls.