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.