Rotating a screw advances a spiraled incline into a surface. The head of a screw functions as a lever, while its threading is just a long incline that has been wrapped around a vertical shaft.
A screw is one of the six classical simple machines, which are basic devices that more sophisticated machines incorporate or build upon. Screws are used most often as simple fasteners because they possess a thread able to supply a tighter seal than nails or pegs. Screws are common machines that make possible a number of mechanical devices and more sophisticated machinery that people use every day.