1. Strength of bolts

Bolt strength is an important indicator of whether the bolt can withstand the rated load. Commonly used strength grades are 4.6, 4.8, 5.6, 8.8, 9.8, 10.9 and 12.9. The number indicates the tensile strength of the bolt, in MPa, and the letters indicate the material and heat treatment method of the bolt.

In actual use, appropriate bolt strength should be selected to ensure that they will not loosen or break during work. It is recommended to use bolts with a tensile strength more than 3 times higher than the required load.

2. Shear force of bolts

The shear force of the bolt refers to the shear force that the bolt bears. Its size is related to factors such as the strength of the bolt, the tightness of the nut, and whether the structure is loose.

The following is a table of strength and shear forces for common strength classes with a bolt diameter m:

Strength grade Strength (MPa) Maximum shear force (kN)

4.6 400 0.28m²
4.8 400 0.30m²
5.6 500 0.44m²
8.8 800 0.78m²
10.9 1000 0.98m²
12.9 1200 1.18m²

3. Frequently asked questions about bolts

1.Why are bolts loose easily?
Loose bolts may be caused by insufficient strength of the bolts, over-tightening or loose nuts, excessive load or excessive vibration. The solution is to replace the bolts with stronger ones, adjust the tightness of the nuts, reduce the load or install a vibration damping device.

2. What are the causes of bolt breakage?

Bolt breakage can be caused by insufficient strength grade, corrosion, fatigue, over-tightening, temperature changes, etc. To avoid bolt breakage, it is necessary to correctly select the bolt strength, prevent corrosion, avoid over-tightening, and handle high or low temperature working environments accordingly.