High strength bolts of high-strength steel, or need to impose a large bolt preload, can be referred to as high strength bolts. High strength bolts used for connecting bridges, rail, high pressure and ultra high pressure equipment. This bolt The fault mostly brittle fracture. applies high strength bolts EHV device, in order to ensure a sealed container, it is necessary to impose the concept of a large number of prestressed high strength bolts 1. prescribed performance level bolts 8.8 high strength bolts and above, known as high-strength bolts. Now the national standard only lists the M39, for large sizes, particularly length of 10 to 15 times greater than the% of domestic production is still short-term high-strength bolts with ordinary bolts distinguish high strength Bolt is to bear the load than ordinary bolts with larger sizes. Ordinary bolt material is Q235 (ie A3) manufacture. High strength bolts of material 35 # steel or other high-quality materials, made after the heat treatment to improve the strength. The difference is the strength of different materials.