Is IS 6649 still valid for use?

No, IS 6649:1972 has been officially withdrawn by BIS. It is superseded by IS 1367 (Part 6).

What bolts should be used with these nuts?

These nuts are designed for use with high strength structural bolts, typically conforming to IS 3757.

What do property classes like '8' and '10' for nuts mean?

The number indicates the proof load stress. A class '8' nut has a nominal proof load stress of 800 MPa, ensuring it can handle the tensile load from a corresponding class 8.8 bolt.

What is a proof load test for a nut?

It is a test where the nut is assembled on a hardened threaded mandrel and subjected to a specified axial tensile load (proof load) to ensure it can withstand service loads without stripping its threads.

IS 6649

: 1972

High strength structural nuts

CurrentSpecializedSpecificationMaterials Science · Fasteners, Bolts and Anchors

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This Indian Standard specifies the requirements for high strength structural nuts of property classes 8 and 10, intended for use in high-strength structural bolting assemblies. It covers the material, dimensions, mechanical properties, testing methods, and marking for nuts of sizes M12 to M36.

Specifies requirements for high strength structural nuts for use with high strength structural bolts.

Quick Reference Values

Proof Load Stress for Property Class 8800 MPa

Proof Load Stress for Property Class 101000 MPa

Hardness Range for Class 8 (HV)180 - 302

Hardness Range for Class 10 (HV)240 - 353

Width Across Flats for M20 Nut32 mm

Practical Notes

This standard has been WITHDRAWN and is superseded in practice by IS 1367 (Part 6). For all new projects, refer to the latest version of IS 1367.

The property class of the nut (e.g., 8) should be compatible with the property class of the bolt (e.g., 8.8). The nut's proof load capacity must be sufficient to handle the bolt's ultimate tensile strength.

Proper marking is crucial for identification on site. A Class 8 nut for M20 will be marked '8M20' or '8 M20'.