Car wheel bolts are generally made of high-strength steel. The strength grade of the bolt wheels is printed on the head of the truck wheel bolts. There are 8.8, 10.9, and 12.9. The larger the value, the higher the strength. Here, 8.8, 10.9, and 12.9 refer to the performance grade label of the bolt, which consists of two numbers, which respectively represent the nominal tensile strength value and yield ratio of the bolt material, generally expressed by "X.Y", such as 4.8, 8.8, 10.9, 12.9 and so on.