Screw is the use of the object of the bevel rotation and friction of the physical and mathematical principles, progressive fastening tools of the tool. Screw is the general statement of Fastener, everyday spoken language. Screws for daily life indispensable industrial necessities: such as cameras, glasses, watches, electronics, such as the use of minimal screw; television, electrical products, musical instruments, furniture and other general screws; As for engineering, construction, bridges, the use of large screws, nuts, traffic apparatus, aircraft, trams, automobiles and so on the size of the screw. Screw in industry has an important task, as long as there is an industry on the Earth, the function of the screw is always important. Screw is the common invention of people's production and life for thousands of years, and according to the field of application, it is the first great invention of mankind. Screws, also someone called it "screws" [Screw] (screws), "Screw" (screw rod). In fact, the screw is a generic term, and screws, screw rod are mutually distinct. Screws are generally called wooden screws; the front end has a pointed, the kind of pitch is larger, generally used for fastening wood parts, plastic pieces. Screw rod is the machine screw (mechanical screw), is the front end of the kind, the pitch is small, evenly, commonly used for fastening metals, machine parts.