The tensile strength is determined by the material and cold and heat treatment method of the bolt, and is used to represent the maximum strength of the bolt when subjected to tension.
The performance level of bolts is generally divided into 10 levels, ranging from 3.6 to 12.9. Among them, the number before the decimal point represents 1/100 of the tensile strength limit of the material, and the number after the decimal point represents 10 times the ratio of the yield limit to the tensile strength limit of the material.
Similarly, there are seven different performance levels for nuts, ranging from 4 to 12. The number represents 1/100 of the minimum stress that the nut is guaranteed to withstand.
For imperial threads, there are three thread grades for external threads, namely 1A, 2A, and 3A grades, while internal threads include 1B, 2B, and 3B grades. The higher the level number, the tighter the fit.
For metric threads, there are three thread grades for external threads: 4h, 6h, and 6g, and three thread grades for internal threads: 5H, 6H, and 7H. The thread fit is best composed of H/g, H/h, or G/h. For refined fasteners such as bolts and nuts, the standard recommends using a 6H/6g fit.
The calculation of bolt tensile strength is generally based on the nominal diameter. The calculation formula is F=σ * A, where F represents tensile strength, σ represents material tensile strength, and A is the effective area. The specific principles can refer to the knowledge of related disciplines such as Materials Mechanics.
In summary, when selecting bolts, it is important to pay attention to their tensile strength level and choose the appropriate bolt level based on specific usage needs to ensure safety and reliability.
