Screw Jacks

A jackscrew is a type of jack that is operated by turning a lead screw. In the form of a screw jack it is commonly used to lift heavy weights, such as the foundations of houses, or large vehicles.
An advantage of jackscrews over some other types of jack is that they are self-locking, which means when the rotational force on the screw is removed, it will remain motionless where it was left and will not rotate backwards, regardless of how much load it is supporting. This makes them inherently safer than hydraulic jacks, for example, which will move backwards under load if the force on the hydraulic actuator is accidentally released.