A screw is a mechanism that converts rotational movement to linear motion, and also a torque (rotational pressure) to a direct pressure.  It is among the six classical simple devices. The most usual kind contains a cylindrical shaft with helical grooves or ridges called threads around the outside.   The screw passes with an opening in an additional object or tool, with threads on the within the hole that fit together with the screw’s threads. When the shaft of the screw is revolved about the stationary threads, the screw relocates along its axis loved one to the tool bordering it; as an example revolving a timber screw compels it right into the timber. In screw devices, either the screw shaft can revolve with a threaded hole in a fixed object, or a threaded collar such as a nut can turn around a fixed screw shaft.   Geometrically, a screw can be considered as a narrow inclined plane twisted around a cylindrical tube. 
Like the various other easy machines a screw can enhance force; a tiny rotational pressure (torque) on the shaft can put in a large axial pressure on the lots. The smaller the pitch (the distance between the screw’s strings), the higher the mechanical benefit (the ratio of outcome to input pressure). Screws are extensively made use of in threaded fasteners to hold items together, and in gadgets such as screw tops for containers, vises, screw jacks as well as screw presses.