ISO 16224:2026

Fasteners — Calculation methods for bolt/nut assemblies — Nut design

Scope

This document specifies calculation methods for nuts designed to be mated with bolts, screws and studs in accordance with ISO 898-1, for use in bolted joints under tensile loading and for tightening with tension and torsion taking into account the three possible failure modes: bolt breaking, bolt thread stripping and nut thread stripping (see Clause 5).
The terms “bolt” and “nut” are used as the general terms in this document for externally threaded fasteners (i.e. bolts, screws and studs) and internally threaded fasteners (i.e. tapped holes), respectively.
This document is primarily applicable to steel hexagon nuts:

with ISO metric thread (coarse pitch and fine pitch, see ISO 68-1);
with diameter/pitch combinations according to ISO 261 and ISO 262;
with thread tolerances according to ISO 965-1 and ISO 965-2;
with nominal thread diameters 5 mm ≤ D ≤ 39 mm, and additionally with D < 5 mm and D > 39 mm (see Annex C);
with a hexagon shape and width across flats s ≥ 1,4D.

The calculation methods are also applicable to non-standard nuts or internally threaded parts with ISO metric threads. However, dimensional factors affecting the rigidity of nuts such as the width across flats, outer diameter of cylindrical nuts or other features (e.g. shape of flange) as well as thread tolerances can affect the loadability of the individual bolt/nut assemblies, see Annex A for influencing factors.