In fact, there are many ways to call hexagonal bolts, how to call them hexagonal bolts, and how to call them hexagonal bolts. It can also be called an outer hexagonal bolt. It all means the same thing. This is just a different habit of the individual. The following is the basic knowledge of the hex bolt specification. 1. There are three types of general bolts: A, B and C. The first two types are special bolts, which are rarely used. Generally speaking, general bolts refer to ?-grade general bolts. 2. Class C bolts are usually used for some temporary connections and connections that must be disassembled. The general bolts used in building construction are m16, m20 and m24. Some thick bolts of mechanical engineering may have larger diameters and special uses. 3. The material of high-strength bolts is different from that of general bolts. High-strength bolts are generally used for permanent connections. Usually M16-M30 is applied. Extra-large high-strength bolts have unstable properties and should be used with caution. 4. The bolt connection of the key components of the building structure is usually made of high-strength bolts. 5. The high-strength bolts manufactured by the processing factory are not divided into working pressure type or friction type. 6. Is it a friction-type high-toughness hexagon bolt or a reduced-type high-strength bolt? In fact, there are differences in design schemes and calculation methods. (1) The ultimate bearing capacity of friction-type high-strength bolts is rolling between plates. (2) The bearing capacity of high-strength bolts is limited by the rolling between the plates and the ineffectiveness of the connection. 7. Friction-type high-strength bolts cannot make full use of the development potential of bolts. In specific applications, friction high-strength bolts are used in particularly critical structures or structures that bear dynamic loads, especially when the load causes internal stress in the opposite direction. At this time, the undeveloped bolt potential difference can be used as a safety reserve. In addition, high-strength bolt connections of rolling bearing types should be used to control costs.