Ordinary bolts can be divided into three grades of A, B, and C according to the production accuracy. A and B grades are refined bolts, and C grade is rough bolts. For connecting bolts for steel structures, unless otherwise specified, they are generally ordinary crude grade C bolts. The processing methods of different grades are different, and the corresponding processing methods are usually as follows: ① The bolts of grade A and B bolts are processed by lathes, with smooth surface and accurate size. The material performance grade is 8.8, the production and installation are complicated, and the price is relatively high. High, rarely used; ②C-level bolts are made of unprocessed round steel, and the size is not accurate enough, and the material performance level is 4.6 or 4.8. Large deformation during shear connection, but convenient installation and low production cost, it is mostly used for tensile connection or temporary fixation during installation.