||Carton packing foam protection Screw is the physical and mathematical principle of the object's inclined plane circular rotation and friction, and is used to tighten the device. Screw is the general term of fasteners, daily colloquial language. Screw is an indispensable industrial necessity in daily life: a tiny screw used in cameras, glasses, clocks, electronics, etc.; General screws for TV, electrical products, Musical Instruments, furniture, etc.; Large screws and nuts are used for engineering, construction and bridge. Traffic instruments, airplanes, trams, automobiles, etc., are used with screws. Screws in industry have important tasks, as long as there is industry on the earth, the function of screws will always be important. Screw is a common invention in people's production and life for thousands of years. In terms of application field, it is the first invention of human. Screws are also called "screws" and "screws". In fact, screws are the general term, and screws, screw are different from each other. Screws are commonly called wood screws; It is the kind with a pointed head at the front, with a large pitch, which is used for fastening wooden parts and plastic parts. The screw rod is machine screw (mechanical screw), is the front flat head of the kind, the pitch is small, uniform, generally used for fastening metal, machine parts.