IS 6649:1972 is the Indian Standard (BIS) for high strength structural nuts. 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.
Overview
- Status
- Current
- Usage level
- Specialized
- Domain
- Materials Science — Fasteners, Bolts and Anchors
- Type
- Specification
- Amendments
- Reaffirmed 1993
Also on InfraLens for IS 6649
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 This standard has been WITHDRAWN and is superseded in practice by IS 1367 (Part 6).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'.
Frequently referenced clauses
Updates & Amendments1 amendment
Consolidated list per BIS. For the text of each amendment, refer to the BIS portal link above.
steelhigh strength steelfastenersnuts
International Equivalents
🌐
International Comparison — Coming Soon
We're adding equivalent international standards for this code.
Key Values5
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
Tables & Referenced Sections
Key Tables
Table 1 - Dimensions for High Strength Structural Nuts
Table 2 - Mechanical Properties of High Strength Structural Nuts
Table 3 - Proof Load Values
Key Clauses
Clause 3 - Material and Manufacture
Clause 4 - Dimensions and Tolerances
Clause 5 - Mechanical Properties
Clause 6 - Tests
Clause 8 - Marking
Frequently Asked Questions4
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No, IS 6649:1972 has been officially withdrawn by BIS. It is superseded by IS 1367 (Part 6).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.
QA/QC Inspection Templates
📋
QA/QC templates coming soon for this code.