Screw (mbth) is a tool to tighten the parts of utensils step by step by using the physical and mathematical principles of circular rotation and friction of the inclined plane of objects. 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.
Zuàntóu is a cutting tool used by general drill or drilling machine to cut round holes. The basic principle of the drill bit is to make the drill bit dress and rotate, cut the workpiece, and then remove the chips from the drilling groove. Commonly used drill bits mainly include twist drill, flat drill, center drill, deep hole drill and casing drill. Although reamers and countersinks cannot drill holes in solid materials, they are customarily classified as drill bits.