ISO 898-2:1992 (EN) Mechanical properties of fasteners — Part 2: Nuts with specified proof load values — Coarse threadProperty classes are specified in ISO 898 series relate to materials and mechanical properties, so that nuts in accordance with ISO 898-2:1992 are matching with bolts, screws and studs specified in ISO 898-1 and with flat washers specified in ISO 898-3, as necessary, in order to design suitable assemblies for a given application.
More parts will be developed in the future for bolts, screws, studs and nuts with sizes above 39 mm.
In order to assure the necessary material strength in relation to property classes:
— Quenched and Tempered nuts (QT) are specified with a minimum carbon content and a minimum tempering temperature, are characterized by a homogeneous martensitic structure;
— Non-Quenched and Tempered nuts (NQT) are also specified with a minimum carbon content but are characterized by a non-quenched microstructure.
Some property classes (in relation to nut style, diameter and coarse or fine pitch thread) specified as NQT may be optionally quenched and tempered as specified in 7.2, and in this case all requirements for QT nuts apply.
For fully loadable non-standard nuts which are to meet the requirements of this ISO 898-2:1992, the relevant style 1 or style 2 is assigned in relation to their minimum design thread height.
Nut load ability is primarily checked by proof load. For nuts with coarse pitch thread and property classes 6 and 8, proof load values have been raised for sizes M27 to M39 due to the latest calculations of Masaya Hagiwara in accordance with the Alexander’s theory. For those nuts it was necessary to develop full strength in relation to the mating bolts, screws and studs specified in ISO 898-1, the difference between the proof loads of ISO 898-2:2012 and the recalculated values being more than 5 %
ISO 898-2:1992 defines the mechanical and physical properties of nuts made of non-alloy steel or alloy steel, for three different nut styles in accordance with 5.1:
— regular nuts (style 1),
— high nuts (style 2),
— thin nuts (style 0),
in combination with:
— coarse pitch thread M5 ≤ D ≤ M39, and fine pitch thread 8 mm ≤ D ≤ 39 mm,
— specified property classes 04, 05, 5, 6, 8, 10 and 12 including proof loads,
and able to be mated with bolts, screws and studs with property classes in accordance with ISO 898-1.
These combinations are based on bolt/nut compatibility, manufacturing processes and market needs. If other combinations are needed, e.g. for nuts designed for particular applications, see ISO/TR 16224.
Nuts conforming to the requirements of ISO 898-2:1992 are tested at the ambient temperature range of 10 °C to 35 °C. It is possible that they do not retain the specified mechanical and physical properties at elevated and/or lower temperatures.
NOTE 1 Nuts conforming to the requirements of ISO 898-2:1992 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 the responsibility of the user to determine the appropriate choice, and consulting an experienced fastener materials expert is recommended outside the range of –50 °C to +150 °C
ISO 898-2:1992 applies to the nuts specified above, with:
— triangular ISO metric thread in accordance with ISO 68-1,
— diameter/pitch combinations in accordance with ISO 261 and ISO 262,
— thread tolerances in accordance with ISO 965-1, ISO 965-2 or ISO 965-5, and
— minimum outside diameter or width across flats s ≥ 1,45D (see Annex B).
For hot dip galvanized nuts, additional requirements are specified in ISO 10684.
This document does not specify requirements for functional properties such as:
— prevailing torque properties (see ISO 2320),
— torque/clamp force properties (see ISO 16047 for test method),
— weldability, or
— corrosion resistance.
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