The screw jack, also known as the mechanical jack, is driven by a manpower through a screw pair, and a screw or nut sleeve can be used as a jacking member. The ordinary screw jack supports the weight by the thread self-locking Conveyor Chain function, and the framework is simple, but the transmission performance is definitely low and the return stroke is gradual. The thread of the self-propelled screw jack has no self-locking action and has a brake. When the brake can be released, the weight could be quickly lowered alone and the return time can be shortened, however the structure of the jack is complicated. The screw jack can support heavy items for a long time, and the utmost lifting capacity has already reached 100 tons, which is widely used. Following the horizontal screw is usually mounted on the low part, the weight could be traversed at a small distance.
Principle of use:
The mechanical jack is among the types of manual lifting tools. Its compact structure makes reasonable use of the rocking of the rocker to rotate the pinion. It is operated by a pair of conical gears to operate a vehicle the screw to rotate and force the lifting sleeve to ensure that the fat rises or decline.
Instructions:
1. Before use, it is necessary to check if the jack is regular, whether the elements are flexible, put lubricating oil, and properly estimate the pounds of the large object. Make use of a jack of appropriate tonnage and steer clear of overloading.
2. Adjust the method of supporting one’s teeth on the rocker. Firstly, turn the rocker directly in the clockwise path by hand to help make the lifting sleeve quickly ascend the top weight.
3. Insert the handle in to the rocker hole, move the deal with up and down, and the weight will rise. When the crimson warning line appears on the lifting 
sleeve, the handle ought to be stopped instantly. If you need to lower the teeth in the opposite direction, the weight will start to fall.
Precautions:
1. Generally keep the surface of the machine clean, verify the internal structure regularly, make the pinion in the rocker versatile and reliable, and lift the lifting sleeve openly.
2. The friction surface between the lifting sleeve and the casing must be oiled at any time. Other oil filling holes should be lubricated regularly.
3. In order to consider the security used, avoid overloading, use illness, it is not appropriate to use multiple units to avoid danger.