What is the difference between hexagon socket head cap screws grade 12.9 and grade 10.9

The performance grade of bolts for steel structure connection is divided into more than 10 grades, such as 3.6, 4.6, 4.8, 5.6, 6.8, 8.8, 9.8, 10.9, 12.9, etc. Among them, the 8.8 grade and above bolts are made of low carbon alloy steel or medium carbon steel and are heat treated (quenched and tempered), commonly known as high strength bolts, and the rest are commonly known as ordinary bolts. The bolt performance grade label consists of two parts, which respectively represent the nominal tensile strength value and yield ratio of the bolt material. For example:

Bolts of performance class 4.6 shall mean:

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

2. The yield ratio of bolt material is 0.6;

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

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

1. The nominal tensile strength of bolt material shall reach 1000MPa;

2. The yield ratio of bolt material is 0.9;

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

The meaning of the performance level of the bolt is the international standard, the same performance level of the bolt, regardless of its material and origin of the difference, its performance is the same, the design of only the performance level can be selected.

Strength grade The so-called 8.8 grade and 10.9 grade refer to the shear stress resistance of bolts of 8.8GPa and 10.9GPa

8.8 Nominal tensile strength 800N/MM2 Nominal yield strength 640N/MM2

General bolts are expressed by "X.Y", X * 100 = the tensile strength of the bolt, X * 100 *(Y/10)= the yield strength of the bolt (because according to the marking regulations: yield strength/tensile strength = Y/10)

such as 4.8 level

Then the tensile strength of this bolt is 400MPa; The yield strength is 400*8/10 = 320MPa.