Screw, in system production, a usually circular cylindrical member with a continuous helical rib, used both as a fastener or as a pressure and movement modifier.
Although the Pythagorean logician Archytas of Tarentum (5th century BC) is the alleged inventor of the screw, the exact date of its first appearance as a beneficial mechanical tool is difficult to understand. Though invention of the water screw is typically ascribed to Archimedes (3rd century BC), proof exists of a similar tool used for irrigation in Egypt at an in advance date. Tornillos screw press, probable invented in Greece within the 1st or 2nd century BC, has been used since the days of the Roman Empire for urgent garments. In the first century AD, timber screws have been used in wine and olive-oil presses, and cutters (faucets) for slicing inner threads have been in use.
These screws stretch when tightened, and the tensile load created clamps the elements collectively. Machine screws have diverse sorts of heads, maximum with screwdriver slots. They are made in smaller sizes than cap screws and bolts.
The setscrew within the Figure fits into a threaded hollow in one member; while tightened, the cup-formed point is pressed right into a mating member (normally a shaft) and stops relative movement. Setscrews also are made with conical and cylindrical factors that suit in matching holes and with slotted and rectangular heads.
A stud is a rod threaded on both ends. It is permanently screwed into one member and clamped by a nut on the other give up.
Self-tapping screws form or cut mating threads in such materials as metals, plastics, glass fibre, asbestos, and resin-impregnated plywood whilst driven or screwed into drilled or cored (solid) holes. The self-tapping screw in the Figure forms threads with the aid of displacing material adjoining to a pilot hole so that it flows around the screw. Thread-slicing tapping screws have reducing edges and chip cavities that produce a mating thread via putting off cloth.
Wood screws are made in a huge variety of diameters and lengths; when the use of the larger sizes, pilot holes are drilled to avoid splitting the wooden. Lag screws are huge wooden screws used to fasten heavy objects to wooden. Heads are either square or hexagonal.