What is the performance class of a Grade 8 carbon steel hex nut?

1. Performance matching logic: The performance class number of the nut corresponds to the strength class of the mating bolt. A Grade 8 nut ensures that when tightened with a Grade 8.8 bolt, the ultimate strength of the entire assembly is not lower than that of the bolt itself, preventing the nut from failing before the bolt.

2. Core performance indicators: Grade 8 nuts of various nominal diameters must meet standard requirements for proof load, hardness, and other parameters. Under standard operating conditions, the hardness range is HRC 25–35; they must also comply with general fastener inspection standards regarding thread precision and dimensional tolerances.

3. Application scenarios: Widely used in general industrial assembly, standard machinery, civil construction, and other applications requiring reliable fastening strength. They are not suitable for extreme operating conditions involving ultra-high pressure, severe impact, or heavy loads.

4. Safety note: Must be paired with bolts of the same specification and matching strength class. Pairing high-strength bolts with lower-grade nuts is prohibited, as this creates a risk of fastening failure, such as stripped threads or nut fracture.