The bolt is a type of fastener consisting of a head and a screw (cylinder with external thread). It needs to be matched with a nut to fasten and connect two parts with through holes. According to the shape of the head: There are hexagonal heads, round heads, square heads, countersunk heads, etc., like hexagonal bolts, carriage bolts, hexagon socket bolts, T bolts, flange bolts, countersunk bolts, square head bolts,

According to relevant standards, the performance grades of carbon steel and alloy steel bolts are divided into more than 10 grades: 3.6, 4.6, 4.8, 5.6, 6.8, 8.8, 9.8, 10.9, 12.9, among which grade 8.8 and above bolts are made of low-carbon alloy steel or medium Carbon steel is heat-treated (quenched and tempered) and is generally called high-strength bolts, and the rest are generally called ordinary bolts. The bolt performance grade label consists of two numbers, which respectively indicate the nominal tensile strength value and the yield ratio of the bolt material. Stainless steel bolts are divided into A1-50, A1-70, A1-80, A2-50, A2-70, A2-80, A3-50, A3-70, A3-80, A4-50, A4-70, A4-80, A5-50, A5-70, A5-80, C1-50, C1-70, C1-110, C4-50, C4-70, C3-80, F1-45, F1- 60. The first letter and number represent the group of stainless steel, and the second and third numbers represent 1/10 of the tensile strength.