By the method of connection and force application: Ordinary bolts and bolts for reamed holes. By head shape: Hexagonal, round, square, countersunk, etc. Hexagonal heads are the most common. Countersunk heads are generally used where a connection is required.
U-bolts are non-standard parts, shaped like a U, and threaded at both ends for use with nuts. They are mainly used to secure tubular objects such as water pipes or sheet objects such as leaf springs in automobiles. Because the way they secure objects resembles a person riding a horse, they are called saddle bolts. By thread length: Fully threaded and partially threaded.
By thread profile: Coarse thread and fine thread. Coarse thread is not shown in the bolt markings. Bolts are classified into eight grades according to their performance: 3.6, 4.8, 5.6, 6.8, 8.8, 9.8, 10.9, and 12.9. Bolts of grade 8.8 and above (including 8.8) are made of low-carbon alloy steel or medium-carbon steel and undergo heat treatment (quenching and tempering), commonly referred to as high-strength bolts. Bolts of grade 8.8 and below (excluding 8.8) are commonly referred to as ordinary bolts.
Ordinary bolts are classified into three grades: A, B, and C, according to their manufacturing precision. Grades A and B are precision bolts, while grade C is a coarse bolt. For connecting bolts used in steel structures, unless otherwise specified, they are generally ordinary coarse grade C bolts. The processing methods differ between grades, typically corresponding to the following: ① Grade A and B bolts have shanks machined on a lathe, resulting in a smooth surface and precise dimensions. Their material performance grade is 8.8. Manufacturing and installation are complex, and the price is high, so they are rarely used. ② Grade C bolts are made from unprocessed round steel, with less precise dimensions. Their material performance grade is 4.6 or 4.8. Shear connections exhibit large deformation but are easy to install and have low production costs. They are often used for tensile connections or temporary fixing during installation
