Hexagon socket head shoulder screws are classified into grades according to the hardness, tensile strength, yield strength, etc. of the screw wire, that is, the grade of hexagon socket bolts, what grade of hexagon socket bolts are. Different grades of hexagon socket bolts are required to correspond to different product materials. Hexagon socket bolts are divided into ordinary and high-strength according to grade strength. Ordinary hexagon socket bolts refer to grade 4.8, and high-strength hexagon socket bolts refer to grade 8.8 or above, including grade 10.9 and grade 12.9. Grade 12.9 hexagon socket bolts generally refer to knurled, natural black hexagon socket head screws with oil. The performance grades of hexagon socket bolts 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, 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), which are generally called high-strength bolts, and the rest are generally called ordinary bolts.

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