Fastener grade

We often have a high-frequency word during maintenance or installation, which is the “performance level” of the bolt. So, what is the bolt level and what does it mean? Today, I will take a look with everyone.

The structural connection bolts 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, bolts of grade 8.8 and above are made of low-carbon alloy steel or medium-carbon steel and are heat-treated ( Quenching and tempering), commonly known as high-strength bolts, the rest are commonly known as ordinary bolts. The bolt performance grade label is composed of two parts of numbers, which respectively represent the nominal tensile strength value and yield ratio of the bolt material. 48 is 4.8.

For example: the bolt of performance grade 4.8, the meaning is:

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

2. The yield ratio of bolt material is 0.8;

3. The nominal yield strength of the bolt material reaches 400 × 0.8 = 320MPa


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

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

2. The yield ratio of bolt material is 0.9;

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


The meaning of bolt performance level is an international standard. Regardless of the difference in material and place of origin, the performance of bolts of the same performance level is the same. Only the performance level can be used for design.

The so-called strength grades of 8.8 and 10.9 refer to the bolts with a shear stress rating of 8. and 10.9GPa 8.8 Nominal tensile strength 800N / MM2 Nominal yield strength 640N / MM2 General bolts are indicated by “XY” for strength * 100 = tensile strength of this bolt, X * 100 * (Y / 10) = yield strength of this bolt (because according to the sign: yield strength / tensile strength = Y / 10, that is, 0.Y is the yield strength ratio )


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

In addition: stainless steel bolts are usually marked as A4-70, A2-70, the meaning is explained separately: there are two main length measurement units in the world today, one is metric system, and the measurement units are meters (m) and centimeters (cm) ), Millimeter (mm), etc., are more commonly used in Southeast Asia such as Europe, China and Japan, the other is English, and the unit of measurement is mainly inches. It is used more in the United States, Britain and other European and American countries.

1. Metric measurement: (decimal system) 1m = 100 cm = 1000 mm

2. Inch measurement: (8 hexadecimal) 1 inch = 8 cents 1 inch = 25.4 mm 3/8 ¢¢ × 25.4 = 9.523, 1/4 ¢¢ The following products are indicated by the number, such as: 4 #, 5 #, 6 #, 7 #, 8 #, 10 #, 12 #.

Post time: Apr-30-2020
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