This standard specifies the requirements for high strength structural nuts of Property Class 8, from sizes M12 to M36. It covers material, chemical composition, mechanical properties, dimensions, testing, and marking for nuts intended for use in high-strength friction-grip and bearing-type bolted connections in steel structures.
Specifies requirements for hexagon high strength structural nuts, complementing high strength structural bolts.
Quick Reference Values
Specified Property Class8
Proof Load Stress (Size > M16 to M36)860 MPa
Hardness Range (HB)188 to 302 HB
Phosphorus Content (Max)0.050 %
Sulphur Content (Max)0.050 %
Chamfering Angle30° to the end face of nut
Practical Notes
Always pair these nuts with high strength bolts as per IS 3757 and hardened washers as per IS 6649 to ensure the integrity of the bolted connection.
The '8' or '8S' marking on the nut face is crucial for on-site verification of the property class. Using a lower-grade nut can lead to catastrophic thread stripping failure under load.
The proof load capacity of the nut is designed to be greater than the ultimate tensile strength of the corresponding bolt, ensuring that in case of overload, the bolt will fail in tension (a more ductile and predictable failure) rather than the nut stripping its threads.