According to the hardness of screw wire, carrying tension, yield strength and so on, there is a grade classification of Hexagon socket bolt, that is, the level of hexagon socket bolt. Different products and materials are required to have different grades of hex socket bolts corresponding to them. Hex socket bolts all have the following grades:

Hexagon socket bolts are divided into ordinary and high strength bolts according to grade strength. Ordinary hex socket bolts refer to class 4.8, high strength hex socket bolts refer to class 8.8 or above, including class 10.9 and class 12.9. Hex socket bolts of grade 12.9 are generally black HEX socket cup head screws with knurling, natural color and oil.

The performance grade of hex socket bolts for steel structure connection is 3.6, 4.6, 4.8, 5.6, 6.8, 8.8, 9.8, 10.9, 12.9, etc. There are more than 10 grades, among which the bolts of grade 8.8 and above are made of low carbon alloy steel or medium carbon steel and heat-treated (quenched, tempered), which are generally called high strength bolts, and the others are generally called ordinary bolts. The bolt performance grade label is composed of two parts, which respectively represent the nominal tensile strength value and the buckling ratio of the bolt material.