GB/T 3098.2-2025 Mechanical properties of fasteners — Part 2: Nuts
1 Scope
This document specifies the mechanical and physical properties of coarse pitch thread and fine pitch thread nuts made of carbon steel or alloy steel, when tested at the ambient temperature range of 10°C to 35°C.
This document applies to nuts:
a) with general purpose thread in accordance with GB/T 192
b) with diameter/pitch combinations in accordance with GB/T 193 and GB/T 9144;
c) with coarse pitch thread M5 to M39, and fine pitch thread M8×1 to M39×3;
d) with thread tolerances according to GB/T 197, GB/T 9145 or GB/T 22028;
e) with specified property classes 04, 05, 5, 6, 8, 10 and 12 including proof load;
f) of three different nut styles (see 5.1): regular nuts (style 1), high nuts (style 2) and thin nuts (style 0);
g) with a minimum outside diameter or width across flats s ≥ 1.45D
h) able to mate with bolts, screws and studs with property classes in accordance with GB/T 3098.1 (see Annex B);
i) intended to be used in applications ranging from –50°C to +150°C, or up to +300°C.
Warning: Nuts conforming to the requirements of this document are tested at the ambient temperature range of 10°C to 35°C and are used in applications ranging from –50°C to +150°C. however, these nuts are also used outside this range and up to +300°C for specific applications. It is possible that they do not retain the specified mechanical and physical properties at lower and/or elevated temperatures. Therefore, it is the responsibility of the user to determine the appropriate choices based on the service environment conditions of the assembly (see also 7.1).
For additional specifications applicable to hot dip galvanized nuts, see GB/T 5267.3.
For nuts designed for particular applications, see GB/Z 32564.
This document does not specify requirements for functional properties such as:
— prevailing torque properties (see GB/T 3098.9);
— torque/clamp force properties (see GB/T 16823.3 for test method);
— weldability;
— corrosion resistance.
2 Normative references
The following normative documents contain provisions which, through reference in this text, constitute provisions of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
GB/T 228.1 Metallic materials - Tensile testing - Part 1: Method of test at room temperature (GB/T 228.1-2010, ISO 6892-1:2019, MOD)
GB/T 230.1 Metallic materials - Rockwell hardness test - Part 1: Test method (GB/T 230.1-2018, ISO 6508-1:2016, MOD)
GB/T 231.1 Metallic materials - Brinell hardness test - Part 1: Test method (GB/T 231.1- 2018, ISO 6506-1:2014, MOD)
GB/T 3098.9 Mechanical properties of fasteners - Prevailing torque type steel nuts (GB/T 3098.9-2020, ISO 2320:2015, MOD)
GBT 3099.4 Terminology of fasteners - Control, inspection, delivery, acceptance and quality (GB/T 3099.4-2021, ISO 1891-4:2018, IDT)
GB/T 4340.1 Metallic materials - Vickers hardness test - Part 1: Test method (GB/T 4340.1-2024, ISO 6507-1:2023, MOD)
GB/T 5267.3 Fasteners - Hot dip galvanized coatings (GB/T 5267.3-2008, ISO 10684:2004, IDT)
GB/T 5779.2 Fasteners - Surface discontinuities - Nuts (GB/T 5779.2-2000, idt ISO 6157-2:1995)
GB/T 16825.1 Metallic materials - Calibration and verification of static uniaxial testing machines - Part 1: Tension/compression testing machines - Calibration and verification of the force-measuring system (GB/T 16825.1-2022, ISO 7500-1:2018, IDT)
GB/T 39310 Fasteners - Types of inspection documents (GB/T 39310-2020, ISO 16228:2017, MOD)
3 Terms and definitions
No terms and definitions are listed in this document.
4 Symbols
For the purposes of this document, the following symbols apply.
D—— nominal thread diameter of the nut (basic major diameter of the internal thread), mm;
dh——hole diameter of the grip, mm;
F——force, N;
FP——proof load, N;
h——thickness of the grip, mm;
m——height of the nut, mm;
mth,design——design thread height of the nut, mm;
P—— pitch of the thread, mm;
s——width across flats, mm;
SP——stress under proof load, MPa.
5 Designation systems
5.1 Nut styles
This document specifies three styles for nuts.
For standard hexagon nuts without flange and without prevailing torque feature, the following limits apply:
— style 1: regular nut with minimum height 0.80D ≤ m min < 0.89D, see Table B.1;
— style 2: high nut with minimum height m min ≥ 0.89D, see Table B.1;
— style 0: thin nut with minimum height 0.45D≤mmin<0.80D.
For other standard nuts (e.g. nuts with flange, prevailing torque nuts, non‑hexagon nuts, etc.), the style shall be addressed in the product standard together with the mechanical properties.
For nuts per drawing, the style shall be addressed in accordance with the minimum design thread height, mth,design, together with the mechanical properties. mth,design is specified in Figure 1 and Table 1. mth,design is the distance between the intersections of the nut chamfer(s) if any or the nut face(s), with the theoretical cylinder representing the nominal thread diameter D.
Contents
Foreword II
Introduction VIII
1 Scope
2 Normative references
3 Terms and definitions
4 Symbols
5 Designation systems
6 Design of bolt and nut assemblies
7 Material, heat treatment, chemical composition and steel microstructure
8 Mechanical and physical properties
9 Inspection
10 Test methods
11 Marking and labelling
Annex A (Normative) Thread dimensions of the proof load test mandrel
Annex B (Informative) Design principles for nuts
Annex C (Informative) Stress under proof load, SP
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