According to the bolts and screws listed in the national standard, it can be seen that the bolts are characterized by three types of heads (except for special bolts such as anchor bolts, union bolts, etc.), Hex Bolt, Flange Bolt and Carriage Bolt, round head bolts Generally, it is a countersunk head bolt with a tenon or a neck. Moreover, the head feature of the screw is basically round, and a groove is opened on the round end face, which has a cross groove and a hexagon socket (including a hexagon socket). Simply put, it can be judged whether it is a bolt or a screw |: the head is round, there is no tenon and the neck head is a screw, and the rest are bolts. This is an intuitive method for us to judge whether it is a bolt or a screw.

A screw (excluding self-tapping screws and wood screws) is a threaded fastener, because the thread profile of self-tapping screws and wood screws is different from that of machine screws, and the thread profile of screws is the same as that of screws. ) The connections composed of fasteners include bolt connections, double-ended stud connections, and screw connections (including fixed screw connections).

The characteristic of screw connection is that the connecting part of the connected part is a through hole, and the bolt connection pair usually includes bolts, nuts and washers.

The characteristic of the double-ended stud connection is that the connecting piece has threaded holes, the other connecting pieces are processed into through holes, and the double-ended connecting pair usually has a double-ended stud, a nut and a washer. This connection is suitable for occasions where bolt connection cannot be used. For example, the connecting piece in the connecting piece is too thick and should not be used as a through hole.

The feature of threaded connection (excluding set screws) is that one of the connected parts also needs to be machined with threaded holes, the other connecting pieces are machined as through holes, and the screws are directly connected to the threaded holes of the connecting piece, but the screw connection pair No need to use nuts, just screws and washers. Structurally, this joint is simpler and more compact than a double-ended stud. It acts like a two screw connection.

Fastening screw connection is to hold the surface of other parts by screwing the end of the screw into the threaded hole of the part, or push it into the corresponding pit, so that the relative position of the two parts is fixed, so that small force and torque can be transmitted .