Strength grade division of high strength bolt

       The full name of high-strength bolt in production is high-strength bolt connection pair, which is not generally referred to as high-strength bolt. According to the installation characteristics, it can be divided into large hexagon head bolt and torsion shear bolt.

       Among them, the torsional shear bolt is only used in grade 10.9. According to the performance grade of high-strength bolt, it can be divided into 8.8 grade and 10.9 grade.

       There are only large hexagon high strength bolts in grade 8.8. In the marking method, the number before the decimal point indicates the tensile strength after heat treatment; the number after the decimal point indicates the yield strength ratio, that is, the ratio of the measured value of yield strength to the measured value of ultimate tensile strength. Grade 8.8 means that the tensile strength of bolt rod is not less than 800MPa, and the yield ratio is 0.8; grade 10.9 means that the tensile strength of bolt rod is not less than 1000MPa, and the yield ratio is 0.9. In the structural design, the diameter of high-strength bolt is generally M16 / M20 / M22 / M24 / M27 / M30, but M22 / M27 is the second choice series, which is mainly M16 / M20 / M24 / M30 under normal conditions.