Screws are indispensable industrial necessities in daily life: such as cameras, glasses, clocks, electronics, etc. used in very small screws; television, electrical products, musical instruments, furniture, etc. of the general screws; as for engineering, construction, bridges use large screws, nuts; traffic appliances, airplanes, trams, cars, etc. are used for large and small screws. Screws have an important task in industry, as long as there is industry on the earth, the function of screws will always be important.