Worm Drives are used when the axis of rotation of a shaft must change direction. Being low-cost, potentially self-locking and providing high gear reductions, Worm Drives provide an effective means of decreasing speed whilst increasing torque.
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.
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.