The performance grades of bolts for steel structure connections are divided into more than 10 grades such as 3.6, 4.6, 4.8, 5.6, 6.8, 8.8, 9.8, 10.9, and 12.9. Among them, the bolts of grade 8.8 and above are made of low-carbon alloy steel or medium-carbon steel and are called high-strength bolts after heat treatment. The rest are called common bolts.

The bolt performance grade label consists of two parts of numbers, which respectively represent the nominal tensile strength value and yield strength ratio of the bolt material. E.g:

The meaning of bolts with performance grade 4.6 is:

1. The nominal tensile strength of the bolt material reaches 400MPa;

2. The yield strength ratio of the bolt material is 0.6;

3. The nominal yield strength of the bolt material reaches 400×0.6=240MPa.

Performance grade 10.9 high-strength bolts, after heat treatment, can reach:

1. The nominal tensile strength of the bolt material reaches 1000MPa;

2. The yield strength ratio of the bolt material is 0.9;

3. The nominal yield strength of the bolt material reaches 1000×0.9=900MPa.

The meaning of bolt performance grade is an international standard. Bolts of the same performance grade have the same performance regardless of the difference in material and origin, and only the performance grade can be selected for design.

The so-called 8.8 and 10.9 strength grades refer to the shear stress grades of the bolts being 8.8GPa and 10.9GPa.

8.8 The nominal tensile strength is 800N/MM2, and the nominal yield strength is 640N/MM2.

General bolts use "X.Y" to indicate the strength. X*100=tensile strength of this bolt, X*100*(Y/10)=yield strength of this bolt (because according to the label: yield strength/tensile strength=Y/10).

Such as grade 4.8, the tensile strength of this bolt is: 400MPa; the yield strength is: 400*8/10=320MPa.

PS: stainless steel bolts are usually marked as A4-70, A2-70, the meaning is explained otherwise.