Screws, also called "screw" (screw), "screw" (screw). In fact, screws are known generically, and screws and screw rods are different from each other. Screws are generally called wood screws; they have a pointed tip and have a large pitch and are generally used to fasten wooden and plastic parts. The screw rod is a machine screw (mechanical screw). It is a kind of screw with a flat front end. The screw pitch is small and uniform. It is generally used to fasten metal and machine parts.
The type of screw, whether it is a tiny screw used for glasses or a large screw used in large-scale heavy-electric engineering, has many types. The main purpose is to use a high degree of industrial product to form a fixed one, and if it is used, it often occurs between teeth and teeth. , Too hard to lock the screw head off, or bad teeth lock failure to meet the conditions of use, are all quality accuracy problems. Screws are "quantity products" and are not hand-made artworks. In mass production, they are intended to provide consumers with high-precision, stable quality and affordable prices. The precision of the screws is usually 6g (2nd grade, U.S. specification "IFI" is 2A teeth), and the crude screw used in construction projects is 8g (3rd grade, "IFI" is 1A teeth). The value of screws is very important. There are examples in the world of bankruptcies caused by poor screw quality. There are also examples of aircraft falling down and vehicles being subverted due to poor screws.