How to choose a bolt property class

The property class on a metric bolt head tells you its strength. The first number is one hundredth of the minimum tensile strength in MPa; the second is the ratio of yield to tensile strength. An 8.8 bolt has a tensile strength of at least 800 MPa and yields at 80% of that.

• 4.6: light-duty, non-critical joints.
• 8.8: the general engineering default for machinery and vehicles.
• 10.9: highly loaded joints where size and weight matter.

Higher classes need matching nuts and controlled tightening. If in doubt, send us the joint details and we will recommend a class.