Screw is a tool to gradually tighten the parts of an object by using the physical and mathematical principles of circular rotation and friction of the inclined plane of the object. Screw is a general term for fasteners. Screws are indispensable industrial necessities in daily life, such as tiny screws used in cameras, glasses, clocks and watches, electronic products, etc. Universal screws for TV sets, electrical products, musical instruments, furniture, etc. As for projects, buildings and bridges, large screws and nuts are used; Transportation equipment, airplanes, trams, cars, etc. There are both large and small screws. Screw plays an important role in industry. As long as there is industry on the earth, the role of screws will always be important. Screw is the same invention in people's production and life for thousands of years. According to the application field, it is the first invention of mankind. Screws are called "screws" (screws) and "screws" (screws).

In fact, screws are universal, and screws and screws are different. Screws are generally called wood screws; It's the kind with a pointed tip at the front end, with a large pitch, which is generally used to fasten wooden parts and plastic parts. Screw is a kind of machine screw (mechanical screw) with a flat head at the front end. It has a small and uniform pitch and is usually used to fasten metal and machine parts.