Bolt performance grades are divided into more than 10 grades, including 3.6, 4.6, 4.8, 5.6, 6.8, 8.8, 9.8, 10.9, and 12.9. Bolts of grade 8.8 and above are made of low carbon alloy steel or medium carbon steel and have been heat treated (quenched, tempered, etc.) Fire), commonly known as high-strength bolts, and the others are commonly known as ordinary bolts. The bolt performance grade label consists of two parts of numbers, which represent the nominal tensile strength value and the yield strength ratio of the bolt material. The number before the decimal point represents 1/100 of the material's overstrength limit, and the number after the decimal point represents 10 times the ratio of the material's yield limit to its tensile strength limit.

For example: high-strength bolts with performance level 10.9, its meaning is:

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

2. The yield 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 internationally accepted standard. Bolts with the same performance grade have the same performance regardless of differences in materials and origins. Only the performance grade can be selected for design.

The performance level of the nut is divided into 7 levels, from 4 to 12. The number roughly represents 1/100 of the minimum stress that the nut is guaranteed to withstand.

The performance grades of bolts and nuts should be used together, such as grade 8.8 bolts and grade 8 nuts.