Bolt Definition and Classification

TIME：

2022-01-10

Bolt: A mechanical part, a cylindrical threaded fastener with a nut. A type of fastener consisting of a head and a screw (a cylinder with external threads), which needs to be matched with a nut to fasten and connect two parts with through holes. This type of connection is called a bolt connection. If the nut is unscrewed from the bolt, the two parts can be separated, so the bolt connection is a detachable connection.

Classification According to the force-bearing mode of the connection: ordinary and with reamed holes. According to the shape of the head: hexagonal head, round head, square head, countersunk head, etc. Among them, the hexagonal head is the most commonly used. Generally, the countersunk head is used in places where connection is required. The English name of the riding bolt is U-bolt. It is a non-standard part. It is U-shaped, so it is also called U-bolt. There are threads on both ends that can be combined with nuts. It is mainly used to fix tubular objects such as water pipes or sheet objects such as car leaf springs. Because the way it fixes objects is like a person riding on a horse, it is called a riding bolt. According to the length of the thread, it is divided into full thread and non-full thread. According to the thread type, it is divided into coarse thread and fine thread. The coarse thread type is not displayed in the bolt mark.

Bolts are divided into eight grades according to performance level: 3.6, 4.8, 5.6, 5.8, 8.8, 9.8, 10.9, and 12.9. Bolts above grade 8.8 (including grade 8.8) are made of low-carbon alloy steel or medium-carbon steel and are heat-treated (quenched + tempered), commonly known as high-strength bolts, and bolts below grade 8.8 (excluding grade 8.8) are generally known as ordinary bolts. Ordinary bolts can be divided into three grades, A, B, and C, according to the manufacturing accuracy. Grades A and B are refined bolts, and grade C is rough bolts. For connecting bolts for steel structures, unless otherwise specified, they are generally ordinary rough grade C bolts. There are differences in the processing methods for different grades, and the corresponding processing methods are usually as follows: ① The bolt rods of grade A and B bolts are processed by lathes, with smooth surfaces and precise dimensions. Their material performance grade is 8.8. They are complicated to make and install, and are expensive, so they are rarely used; ② Grade C bolts are made of unprocessed round steel, with less precise dimensions, and their material performance grade is 4.6 or 4.8. They have large deformation during shear connection, but are easy to install and have low production costs. They are mostly used for tensile connections or temporary fixation during installation.

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