Chinese standard for hexagon socket head screws.Standard
number for the national standard GB70-1985, there are many
specifications, commonly used specifications are 3*8, 3* 10,3 *
12,3 * 12,3 * 16,3 * 20,3 * 25,4 * 10,4 * 12,4 * 30,4 * 5, 5* 10,5 *
12,5 * 16,5 * 25,6 * 12,6 * 14,6 * 16,6 * 25,8 * 14,8 * 16,8 * 20,8
* 15, 8* 35,8 *40 and so on.
Hexagon socket bolts according to the hardness of the screw wire, tension, yield strength is a grade classification, that is, the level of hexagon socket bolts, hexagon socket bolts is what level.Different product materials require different grades of hexagon socket bolts corresponding to it, all hexagon socket bolts have the following grades:
Hexagon socket bolts are classified into ordinary and high strength according to grade strength.Ordinary hexagon socket bolts refer to grade 4.8, while high-strength hexagon socket bolts refer to grade 8.8 or above, including grade 10.9 and 12.9.Hexagon socket bolts of class 12.9 generally refer to black hexagon socket cup head screws with knurled, natural color and oil.
Hexagon socket bolts used for steel structure connection have more than 10 grades, including 3.6, 4.6, 4.8, 5.6, 6.8, 8.8, 9.8, 10.9 and 12.9, of which 8.8 and above bolts are made of low carbon alloy steel or medium carbon steel and have been heat treated (quenching and tempering). They are generally referred to as high-strength bolts and the rest are ordinary bolts.The grade of bolt performance is composed of two Numbers, which respectively represent the nominal tensile strength and the ratio of buckling strength of bolt materials.