1. There are three kinds of ordinary bolts: A, B and C. The first two are refined bolts, less used. Generally speaking, ordinary bolts refer to C-class ordinary bolts.

2. In some temporary connections and connections that need to be disassembled, Class C ordinary bolts are commonly used. The common bolts used in building structures are M16, M20 and M24. Some machinery industry rough bolt diameter may be relatively large, special use.

3. The material of  is different from that of ordinary bolts. High strength bolts are generally used for permanent connections. M16 to M30 are commonly used. Oversized high-strength bolts are unstable and should be used with caution.

4. The bolt connection of the main components of the building structure is generally connected by high-strength bolts.

5. High strength bolts manufactured by the factory are not divided into pressure type or friction type.

6. Whether it is a friction type high-strength outer  and a pressure type high-strength bolt is actually a difference in design calculation method:

(1) Friction type high-strength bolts take sliding between plates as the limit state of carrying capacity.

(2) The pressure type high-strength bolt takes the sliding between plates as the normal limit state, and the connection failure as the limit state of the carrying capacity.

7. Friction type high-strength bolts can not give full play to the potential of bolts. In practical applications, for very important structures or structures bearing dynamic loads, especially when the load causes reverse stress, the Mohong type high strength bolt should be used, and the untapped bolt potential can be used as a safety reserve. In addition, pressure type high-strength bolt connection should be used to reduce the cost.