Scissor jacks are small in size, low in price, and have the ability to support small cars. They occupy a certain market share in car jacking jacks. However, it should be noted that the self-locking ability of this type of jack is relatively low, which means its support time is relatively short. When changing tires or repairing cars, it is necessary to make quick decisions to avoid situations where the jack's support is insufficient and the vehicle falls.

The self-locking principle used in scissor jacks is the friction self-locking principle. No matter how much gravity is applied above, it will remain stationary on the inclined surface and will not slide down. The weight supported by the jack is added to the screw and the groove cover. When the jack is raised, the center of gravity of the weight changes from the flat surface to the inclined surface. At this time, the thread lift angle is less than or equal to the friction angle between the screw and the groove, which can achieve a certain self-locking ability.

Under the heavy pressure of heavy objects, we can still rotate the handle of the scissor jack to make the gears rotate and continue to raise the weight, but we cannot let the jack remain in a static supporting state for a long time, as the mechanical strength of this type of jack component is relatively small.