A screw thread is a helical groove formed on an internal or external diametrical surface and is described by various terms including pitch, root, crest, flank and major diameter. These terms are described here.
Screw Jacks are found wherever there is a need to lift, position and hold load. A Screw Jack (also known as a Jack Screw, a Worm Screw Jack, a Machine Screw Jack or a Lead Screw Jack) is a devise used to convert rotational motion into linear motion.
Mechanical screw jacks and linear actuators are increasingly becoming the preferred choice of actuation over the equivalent hydraulic or pneumatic systems.