Abstract: A screw-and-nut mechanism comprises a supporting seat, one or more semi-nuts and the actuating member thereof, characterized in that the engagement of internal thread on the semi-nut with external threa on the screw is started elastically, then completed and locked by a positive element, and that the disengagement thereafter of the related elements is accomplished positively. Such a mechanism can be used in various kinds jacks, vices, sliding tables of machine tools, as well as other devices which is driven by a screw and desired to pas through its return travel quickly.

Abstract: This invention relates to a new type of screw-and-nut mechanism comprising a screw stem supported in a structure, the screw stem is to engage with a partially threaded nut also contained in the structure and actuated by a lifting means to effect the quick meshing and disengagement of the nut and the screw stem. With the inclusion of a locking device the screw stem can be made to advance and retract slowly as well as quickly. The merit of not requiring the screw stem to move up and down makes in interchangeable with other mechanisms; the three-point-contained feature enables the screw-and-nut mechanism to sustain large axial loads. Its simple structure and easy operation ensures its wide application in bench vices, parallel-jaw vices and sliding tables of machine tools and all kinds of screw-driven devices requiring fast translational motion.