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Screw classification is:

1. The grade of bolt performance, that is, the grade of bolt performance for steel structure connection, is divided into more than 10 grades, such as 3.6, 4.6, 4.8, 5.6, 5.8, 6.8, 8.8, 9.8, 10.9 and 12.9. The performance grades of bolts used in connection of steel structures can be 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. The bolts of grade 8.8 and above are made of low-carbon alloy steel or medium-carbon steel and are heat-treated (quenched and tempered). They are collectively referred to as high strength bolts, and the rest are collectively referred to as ordinary bolts. The grade label of bolt performance consists of two parts, which represent the nominal tensile strength and yield strength ratio of bolt material.

2. The performance grades of bolts used in connection of steel structures 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 heat-treated (quenched and tempered), commonly known as high-strength bolts, and the rest are commonly referred to as ordinary bolts. The grade label of bolt performance consists of two parts, 

which represent the nominal tensile strength and yield strength ratio of bolt material. For example, a bolt with a performance grade of 4.6 means:

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

2. The yield-strength ratio of bolt material is 0.6.

3. The nominal yield strength of bolt material reaches 400 x 0.6=240MPa grade.

The material of high strength bolt of grade 10.9 after heat treatment can reach:

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

2. The yield-strength ratio of bolt material is 0.9.

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