The numbers on the screw head of the Heavy Hex Bolt play a key role. Why can't bolts be used at will? Because when the screw is used, we not only have to consider whether the basic parameters such as the thread and length of the bolt are consistent, but also consider the performance parameters such as the tensile strength and yield strength of the bolt. The number on the bolt head reflects the tensile and yield strength.

The number "4.8" on the head of the bolt refers to a bolt with a performance level of 4.8, and its specific meaning is:

1. The nominal tensile strength of the bolt material reaches 400MPa;

2. The yield-strength ratio of the bolt material is 0.8 (80% of the tensile strength is the yield point);

3. The nominal yield strength of the bolt material is 400×0.8=320MPa.