A screw jack is also known as a screw transmission mechanism. Its primary function is to convert rotational motion into linear motion, or vice versa. These mechanisms serve various purposes: some are primarily designed for transmitting motion (such as the feed screws on machine tool worktables), while others are used to adjust the relative positioning of components. Screw jacks can be broadly classified into two types: those utilizing sliding friction mechanisms and those utilizing rolling friction mechanisms. The sliding screw-nut mechanism features a simple structure, is easy to manufacture, and offers low production costs; furthermore, it possesses a self-locking capability. However, its drawbacks include high frictional torque and low transmission efficiency. In contrast, while the ball screw-nut mechanism is structurally complex, entails higher manufacturing costs, and lacks a self-locking function, its significant advantages include minimal frictional torque, high transmission efficiency, high precision, excellent system rigidity, motion reversibility, and a long service life. A screw jack typically consists of a worm gear reducer and a lead screw; its speed-reduction component is a worm drive, which utilizes a worm to drive a worm wheel, thereby achieving speed reduction. The worm wheel effectively functions as the nut for the lifting screw, forming a mated pair with it.

The lifting speed of a screw jack is calculated by dividing the input rotational speed of the worm by the reduction ratio of the worm gear set, and then multiplying the result by the pitch of the lead screw. Due to their structural design, these screw jacks typically utilize grease for lubrication. However-regarding maintenance and upkeep-certain product series are designed to use lubricating oil instead of grease; these oil-lubricated models offer distinct advantages, such as a longer service life and more stable operation, compared to their grease-lubricated counterparts.