Bolt materials are mainly divided into 10 strength grades, ranging from 3.6 to 12.9. Grade 8.8 and above are high-strength bolts, widely used in critical structures such as bridges and high-pressure equipment.
These grades are represented in the form "X.Y". The first digit (X) represents 1/100 of the nominal tensile strength (in MPa), and the second digit (Y) represents the yield strength ratio of 10. For example:
4.8 grade: Tensile strength approximately 400MPa, yield strength 320MPa, a common bolt, often used for general mechanical connections;
8.8 grade: Tensile strength 800MPa, yield strength 640MPa, a common high-strength bolt, mostly used in main building structures;
10.9 grade: Tensile strength 1000MPa, yield strength 900MPa, suitable for high-load scenarios such as wind power and heavy equipment;
12.9 grade: Tensile strength 1200MPa, yield strength 1080MPa, an ultra-high-strength bolt, used in extreme working conditions.
