According to the bolts and screws listed in the national standard, it can be seen that the bolt is characterized by three types of head (except for special bolts such as anchor bolts and union bolts), hexagon head screws, square heads (including T-shaped bolts) and round heads. Round head bolts are generally countersunk bolts with tenons or necks. Moreover, the head feature of the screw is basically circular, and a groove is cut on the circular end surface, which is provided with a cross groove and a hexagonal socket hole (including a hexagonal socket flower hole). Simply put, we can judge whether it is a bolt or a screw |: the head is round, no tenon and neck are screws, and the rest are bolts. This is an intuitive way to judge whether it is a bolt or a screw.

Screw (excluding self tapping screw and wood screw) is a kind of threaded fastener. Because the thread tooth type of self tapping screw and wood screw is different from that of machine screw, the thread tooth type of screw is the same as that of screw. The connection composed of fasteners includes bolt connection, double head stud connection and screw connection (including fixed screw connection).

The connection of China Hex socket screws manufacturers is characterized by that the connected parts are through holes, and the bolt connection pairs usually include bolts, nuts and washers.

The double headed stud connection is characterized in that the connecting piece has a threaded hole, the other connecting pieces are processed as through holes, and the double headed connecting pair usually has double headed studs, nuts, and washers. This connection is applicable to the situation where bolt connection cannot be used. For example, the connection pieces in the connection pieces are too thick to make through holes.

The threaded connection (excluding the set screw) is characterized in that one of the connected parts also needs to process the threaded hole, the other connecting parts are processed as through holes, and the screw is directly connected with the threaded hole of the connecting part, but the screw connection pair does not need to use a nut, only screws and washers. In structure, this joint is simpler and more compact than double ended studs. Its function is similar to that of two screws.

The fastening screw connection is used to screw the end of the screw into the threaded hole of the part to counter the surface of other parts, or to jack into the corresponding pit to fix the relative position of the two parts, so that small forces and moments can be transmitted.