Screw is just a general term for fasteners, including bolts, screws and nuts. Nuts with internal thread holes are generally oblate hexagonal cylinders, and some are oblate square cylinders or oblate cylinders, which are matched with bolts, studs or machine screws to tightly connect two parts to make them a whole;

As long as the threaded fastening bolt is composed of a head and a screw, that is, a cylinder with external threads, it needs to be equipped with a nut to fasten two parts with through holes;

This connection form is called bolt connection. If the nut is unscrewed from the bolt, the two parts can be separated, so the bolt connection is detachable.