in machine construction, a usually circular cylindrical member with a continuous helical rib, used either as a fastener or as a force and motion modifier.

Although the Pythagorean philosopher Archytas of Tarentum (5th century BC) is the alleged inventor of the screw, the exact date of its first appearance as a useful mechanical device is obscure. Though invention of the water screw is usually ascribed to Archimedes (3rd century BC), evidence exists of a similar device used for irrigation in Egypt at an earlier date. The screw press, probably invented in Greece in the 1st or 2nd century BC, has been used since the days of the Roman Empire for pressing clothes. In the 1st century AD, wooden screws were used in wine and olive-oil presses, and cutters (taps) for cutting internal threads were in use.

A stud is a rod threaded on both ends. It is permanently screwed into one member and clamped by means of a nut on the other end.

Wood screws are made in a wide variety of diameters and lengths; when using the larger sizes, pilot holes are drilled to avoid splitting the wood. Lag screws are large wood screws used to fasten heavy objects to wood. Heads are either square or hexagonal.

Screws that modify force and motion are known as power screws. A screwjack converts torque (turning moment) to thrust. The thrust (usually to lift a heavy object) is created by turning the screw in a stationary nut. By using a long bar to turn the screw, a small force at the end of the bar can create a large thrust force. Workpiece tables on machine tools are moved linearly on guiding ways by screws that rotate in bearings at the ends of the tables and mate with nuts fixed to the machine frame. A similar torque-to-thrust conversion can be obtained by either rotating an axially fixed screw to drive a rotationally fixed nut along the screw or by rotating an axially fixed nut to drive a rotationally fixed screw through the nut.