The performance grades of internal hexagonal bolts used for steel structure connection are divided into more than 10 grades, including 3.6, 4.6, 4.8, 5.6, 6.8, 8.8, 9.8, 10.9, 12.9, etc. Among them, bolts of grade 8.8 and above are made of low-carbon alloy steel or medium carbon steel and heat treated (quenched and tempered), commonly referred to as high-strength bolts, and the rest are referred to as ordinary bolts. The bolt performance grade label consists of two parts of numbers, representing the nominal tensile strength value and yield strength ratio of the bolt material.

Hexagon bolts are classified according to the hardness, tensile strength, yield strength, etc. of the screw wire, which is the grade of the hexagon bolt and what grade the hexagon bolt is. Different grades of hexagonal bolts are required for different product materials, and all hexagonal bolts have the following grades: