There are many different names for the outer hexagonal bolt, for example, it can be called the outer hexagonal bolt, for example, it can be called the outer hexagonal bolt. It can also be called an outer hexagonal bolt. This all means the same thing. It's just that personal habits are different. After hot galvanizing surface treatment, anti-corrosion effect is achieved. 1. common bolts are divided into a, b and c. The first two are refined bolts, which are seldom used. Generally speaking, ordinary bolts refer to Class C ordinary bolts. 2. Class C common bolts are commonly used in some temporary connections and connections requiring disassembly. Common bolts commonly used in building structures are M16, M20 and M24. Some crude bolts in the mechanical industry may have large diameters and special purposes. high strength friction grip bolt 3. The material of high strength bolt is different from that of ordinary bolt. High strength bolts are generally used for permanent connections. Commonly used are M16~M30.