The main purpose of screws is to make industrial products form a fixed whole. In use, it often happens that the teeth cannot be closely connected with each other, the screw head breaks if the screws are locked too hard, or the teeth cannot be locked tightly due to poor tooth patterns, which is a problem of accuracy. Screws are "mass products", not handmade works of art. In mass production, they are supplied to consumers for the purpose of achieving high precision, stable quality and popular price.

Screws are tools that use the physical and mathematical principles of the circular rotation of the inclined plane of objects and the friction force to tighten the artifacts and parts step by step. Screw is the common expression of fastener, and it is a common colloquialism. Screws are indispensable industrial necessities in daily life: such as tiny screws used in cameras, glasses, clocks and watches, electronics, etc; General screws for TV, electrical products, musical instruments, furniture, etc; Large screws and nuts are used for projects, buildings and bridges; Transportation appliances, airplanes, trams, automobiles, etc. are used for large and small screws.