Bolt: A type of fastener consisting of a head and a screw (a cylinder with external threads), used in conjunction with a nut to fasten two parts with a through hole.

This type of connection is called bolted connection. If the nut is unscrewed from the bolt, the two parts can be separated, so the bolt connection is a detachable connection.

Bolt classification

1. According to the force mode of the connection, the bolts used for ordinary and reamed holes should be matched with the size of the holes and used when subjected to transverse force. (The unthreaded part of the reamed hole bolt is the same as the basic size of the hole wall, which belongs to the coordination, and the bolt has the positioning function in addition to the tightening function; The unthreaded part of the ordinary bolt is different from the basic size of the hole wall and does not belong to the fit. On the drawing, it is that the reamed hole bolt and the hole wall are composed of a line; The ordinary bolt and hole wall are composed of two lines.

2, according to the shape of the head with hexagonal head, round head, square head, countersunk head and so on. Generally, the countersunk head is used in places where the surface is smooth without protrusions after connection, because the countersunk head can be screwed into the part. Round heads can also be screwed into parts. The tightening force of the square head can be larger, but the size is large, and the hexagonal head is the most commonly used.

In addition, in order to meet the needs of locking after installation, there are holes in the head and holes in the rod part, which can make the bolt not loose when it is subjected to vibration.

Some bolts do not screw the rod to be thin, called thin waist bolts, this bolt is conducive to the connection of variable forces.

There are special high-strength bolts on the steel structure, the head will be larger, and the size will also change.

In addition, there are special uses: T-slot bolts, the most used on the machine tool fixture, the shape is special, and the two sides of the head should be cut off. Anchor bolts, used for machine and ground connection fixing, there are many shapes, U-shaped bolts and so on.

There are special studs for welding, one end has a thread and one end does not, which can be welded on the part, and the other side directly screws the nut.

The meaning of bolt performance class

Bolts for steel structure connection performance grades are 3.6, 4.6, 4.8, 5.6, 6.8, 8.8, 9.8, 10.9, 12.9 and other more than 10 grades, of which 8.8 and above bolts are made of low carbon alloy steel or medium carbon steel and heat treatment (quenching, tempering), generally known as high strength bolts, and the rest are called ordinary bolts. The bolt performance grade label consists of two parts, which respectively represent the nominal tensile strength value and the flexure ratio of the bolt material. For example:

A bolt with a performance rating of 4.6 is defined as:

1, bolt material nominal tensile strength of 400MPa level;

2. The bending ratio of bolt material is 0.6;

3, the nominal yield strength of the bolt material is 400×0.6=240MPa

Performance class 10.9 high strength bolt, the material after heat treatment, can achieve:

1, bolt material nominal tensile strength of 1000MPa level;

2. The bending ratio of bolt material is 0.9;

3, the nominal yield strength of the bolt material is 1000×0.9=900MPa

The meaning of bolt performance grade is an international standard, the same performance grade of bolts, regardless of the difference in material and origin, its performance is the same, the design can only choose the performance grade. The so-called 8.8 and 10.9 strength grades refer to the shear stress grades of the bolts of 8.8GPa and 10.9GPa, and the s of 10.9s indicates the steel structure.