1. According to the stress mode of connection, there are common and reaming holes The bolts used for reaming holes shall match the size of the holes, and shall be used under lateral force.

2. According to the head shape, there are hexagonal head, round head, square head, countersunk head, etc. generally, countersunk head is used where the surface is required to be smooth without protrusion after connection, because countersunk head can be screwed into parts. The round head can also be screwed into the part. The tightening force of square head can be larger, but the size is large. Hexagon head is the most commonly used. In addition, in order to meet the needs of locking after installation, there are holes in the head and in the rod. These holes can prevent the bolt from loosening when it is vibrated. Some bolts without thread should be made thin, which is called thin waist bolt This kind of bolt is beneficial to the connection under variable force. There are special high-strength bolts on the steel structure The head will be bigger Dimensions also vary. In addition, it has special use: T-shaped groove bolt is used, which is most used on machine tool fixtures. It has a special shape, and both sides of the head should be cut off. Anchor bolts are used to connect and fix the machine to the ground. There are many shapes, such as U-shaped bolts, etc. There are also special studs for welding, with threads on one end and no threads on the other, which can be welded to the parts, and the nuts can be screwed directly on the other side. The meaning of bolt performance grade means that the performance grade of bolts for steel structure connection is divided into more than 10 grades, including 3.6, 4.6, 4.8, 5.6, 6.8, 8.8, 9.8, 10.9 and 12.9. Among them, the bolts of grade 8.8 and above are made of low carbon alloy steel or medium carbon steel and heat treated (quenched and tempered), which are generally referred to as high-strength bolts, and the rest are generally referred to as ordinary bolts. The bolt performance grade is composed of two numbers, which respectively represent the nominal tensile strength value and yield strength ratio of the bolt material.