When I was in school, the geometric principle that the two waists of an isosceles triangle remain unchanged and the height line is raised when the base is shortened was only a textbook knowledge. Now that I have entered society and had the opportunity to come into contact with mechanical equipment such as scissor jacks, I have discovered that simple mathematical principles can still be applied in practice to help us lift large tonnage heavy objects.

Limit lines are marked on jack equipment such as screw jacks and hydraulic jacks with lifting sleeves. These limit lines are the lifting limit position of the jack. Shear jacks have a simple structure and relatively few internal components, let alone lifting sleeves. Will upper limit devices still be installed to help people reduce the risk of operational errors?

We cannot expect scissor jacks to lift loading trucks, so they are usually used to lift ordinary cars. Ordinary cars have lower chassis, so most of these jacks do not have limit devices. When lifting, the lifting height of the jack should not exceed 3/4 of the height of the screw or rack.