Screw is a tool that uses the physics and mathematical principles of the circular rotation and friction of the bevel of the object to gradually tighten the objects and parts. Screws are a generic term for fasteners, spoken daily. Screws are an indispensable industrial necessity in daily life: very small screws used in cameras, glasses, clocks, electronics, etc .; general screws for televisions, electrical products, musical instruments, furniture, etc .; as for engineering, architecture, bridges, large Screws and nuts; transportation equipment, airplanes, trams, cars, etc. are large and small screws. Screws have important tasks in industry. As long as there is industry on the earth, the function of screws is always important. The screw is a common invention in the production and life of people for thousands of years. According to the field of application, it is the first invention of mankind.