What does the property class of a nut indicate?

It indicates the maximum bolt property class with which the nut can safely mate. For example, a Class 8 nut can mate with a Class 8.8 bolt.

Is hardness testing sufficient for nut acceptance?

No, proof load testing is the primary and decisive acceptance criterion. Hardness testing is considered secondary.

What is the maximum thread size covered in this standard?

The standard covers nominal thread diameters up to and including M39.

IS 1367 Part 3

: 2002

Technical Supply Conditions for Threaded Steel Fasteners - Part 3: Mechanical Properties of Fasteners Made of Carbon Steel and Alloy Steel - Bolts, Screws and Studs

CurrentFrequently UsedSpecificationMaterials Science · Steel and Reinforcement

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This part of IS 1367 specifies the mechanical and physical properties of bolts, screws, and studs made of carbon and alloy steel when tested at ambient temperatures. It establishes the globally standardized property class designation system (e.g., 4.6, 8.8, 10.9) and details testing methods for assessing ultimate tensile strength, yield strength, proof load, and hardness.

Specifies the mechanical properties of bolts, screws, and studs made of carbon steel and alloy steel.

Quick Reference Values

applicable thread diameterUp to M39

regular nut property classes4, 5, 6, 8, 9, 10, 12

thin nut property classes04, 05

temperature rangeTested at 10 to 35 °C

Key Formulas

F = As × Sp (Proof Load = Nominal stress area × Proof stress)

Practical Notes

Always match the nut property class to or higher than the bolt property class (e.g., use a Class 8 nut for a Class 8.8 bolt) to prevent thread stripping.

In case of a dispute, the proof load test is the decisive acceptance criterion over hardness testing.

This standard applies to standard nuts but excludes those requiring special properties like weldability, extreme temperature resistance, or corrosion resistance.