Screw type, whether it's glasses with micro screw or large heavy electrical engineering to use the size of the screw it is a lot of more phyletic, the main purpose in the height of the industrial products of the fixed one, if in use often occur between tooth and tooth can't close, too hard lock, screw head is broken off, or bad tooth grain lock is not tight failed to meet conditions of use, all for the quality of the precision problem.Screws are "quantity products", not hand-made works of art, in the mass production, to achieve high precision and stable quality and popular price supply to consumers for the purpose.The precision of screws is usually 6g, and that of rough screws used in construction projects is 8g.

The main categories include ordinary screws, self-tapping screws and expansion screws.