ISO 8641:2008

Aerospace — Self-locking nuts with maximum operating temperature greater than 425 degrees C — Procurement specification

ISO 8641:2008 specifies the required characteristics for metric self-locking nuts, with MJ thread, for use in aerospace construction at a maximum temperature greater than 425 °C. ISO 8641:2008 is applicable to nuts as defined above, provided that reference is made to this International Standard in the relevant definition document.

Aéronautique et espace — Écrous à freinage interne dont la température maximale d'utilisation est supérieure à 425 degrés C — Spécification d'approvisionnement

General Information

• Status: Published
• Publication Date: 25-Aug-2008
• ICS: 49.030.30 - Nuts
• Technical Committee: ISO/TC 20/SC 4 - Aerospace fastener systems
• Drafting Committee: ISO/TC 20/SC 4 - Aerospace fastener systems
• Current Stage: 9093 - International Standard confirmed

Relations

• Revises: ISO 8641:1987 - Aerospace — Self-locking nuts with maximum operating temperature greater than 425 degrees C — Procurement specification
• Effective Date: 15-Apr-2008

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 8641
Second edition
2008-09-01
Aerospace — Self-locking nuts with
maximum operating temperature greater
than 425 °C — Procurement specification
Aéronautique et espace — Écrous à freinage interne dont la
température maximale d'utilisation est supérieure à 425 °C —
Spécification d'approvisionnement

Reference number
©
ISO 2008
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ii © ISO 2008 – All rights reserved

Contents Page
Foreword. iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions. 2
4 Quality assurance. 4
4.1 General. 4
4.2 Qualification inspection and test conditions. 4
4.3 Production acceptance inspection and test conditions. 4
4.4 Use of “statistical process control (SPC)”. 5
5 Technical requirements . 5
Annex A (normative) Type of permissible surface discontinuities (see 5.1.3) . 21
Annex B (informative) Cross-sectional area and formulae for axial loads (see Table 3) . 22

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 8641 was prepared by Technical Committee ISO/TC 20, Aircraft and space vehicles, Subcommittee SC 4,
Aerospace fastener systems.
This second edition cancels and replaces the first edition (ISO 8641:1987) which has been technically revised.
iv © ISO 2008 – All rights reserved

INTERNATIONAL STANDARD ISO 8641:2008(E)

Aerospace — Self-locking nuts with maximum operating
temperature greater than 425 °C — Procurement specification
1 Scope
This International Standard specifies the required characteristics for metric self-locking nuts, with MJ thread,
for use in aerospace construction at a maximum temperature greater than 425 °C.
It is applicable to nuts as defined above, provided that reference is made to this International Standard in the
relevant definition document.
2 Normative references
The following referenced documents are indispensable for the application 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.
ISO 691, Assembly tools for screws and nuts — Wrench and socket openings — Tolerances for general use
ISO 1463, Metallic and oxide coatings — Measurement of coating thickness — Microscopical method
ISO 2859-1:1999, Sampling procedures for inspection by attributes — Part 1: Sampling schemes indexed by
acceptable quality level (AQL) for lot-by-lot inspection
ISO 4288, Geometrical Product Specifications (GPS) — Surface texture: Profile method — Rules and
procedures for the assessment of surface texture
ISO 5855-2, Aerospace — MJ threads — Part 2: Limit dimensions for bolts and nuts
ISO 7403, Aerospace — Spline drives — Wrenching configuration — Metric series
ISO 7870-1, Control charts — General guidelines
ISO 7966, Acceptance control charts
ISO 8258, Shewhart control charts
ISO 8642, Aerospace — Self-locking nuts with maximum operating temperature greater than 425 °C — Test
methods
ISO 8788, Aerospace — Nuts, metric — Tolerances of form and position
ISO 9199, Aerospace — Nuts, bihexagonal, self-locking, MJ threads, classifications: 1 100 MPa (at ambient
temperature)/425 °C, 1 100 MPa (at ambient temperature)/650 °C, 1 210 MPa (at ambient
temperature)/425 °C, 1 210 MPa (at ambient temperature)/730 °C, 1 550 MPa (at ambient
temperature)/235 °C, 1 550 MPa (at ambient temperature)/425 °C and 1 550 MPa (at ambient
temperature)/600 °C — Dimensions
ISO/TR 13425, Guidelines for the selection of statistical methods in standardization and specification
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
definition document
document specifying all the requirements for nuts, i.e.:
— metallurgical;
— geometrical and dimensional;
— functional (strength and temperature classes)
NOTE The definition document can be an International Standard, a national standard, an in-house standard or a
drawing.
3.2
finished nut
nut ready for use, inclusive of any possible treatments and/or surface coatings, as specified in the definition
document
3.3
batch
definite quantity of some commodity manufactured or produced under conditions which are presumed to be
uniform
NOTE For the purposes of this International Standard, a batch is a quantity of finished nuts, of the same type and
same diameter, produced from a material obtained from the same melt, manufactured in the course of the same
production cycle, following the same manufacturing route and having undergone all the relevant heat treatments and
surface treatments.
3.4
crack
rupture in the material which may extend in any direction and which may be intercrystalline or transcrystalline
in character
3.5
seam
open surface defect resulting from extension of the metal
3.6
lap
folding over of unwelded metal that can arise when the material is formed (drawing) or in the finished product
(pressing or forging)
3.7
inclusions
non-metallic particles originating from the material manufacturing process
NOTE These particles can be isolated or arranged in strings.
3.8
critical defect
defect that, according to judgement and experience, is likely to result in hazardous or unsafe conditions for
individuals using, maintaining or depending upon the considered product, or that is likely to prevent
performance of the function of a major end item
2 © ISO 2008 – All rights reserved

3.9
major defect
defect other than critical, that is likely to result in a failure or to reduce materially the usability of the considered
product for its intended purpose
3.10
minor defect
defect that is not likely to reduce materially the usability of the considered product for its intended purpose, or
that is a departure from established specifications having little bearing on the effective use or operation of this
product
3.11
sampling plan
plan according to which one or more samples are taken in order to obtain information and possibly reach a
decision
NOTE For the purposes of this International Standard, each sampling plan specifies the number of nuts to be
1)
inspected as a function of the size of the batch and the acceptance number [number of defective items acceptable (Ac)] .
3.12
simple random sampling
sampling of n items from a population of N items in such a way that all possible combinations of n items have
the same probability of being chosen
3.13
acceptance quality limit
AQL
maximum percent defective (or the maximum number of defects per hundred units) that, for purposes of
sampling inspection, can be considered satisfactory as a process average
NOTE Variant: quality limit which in a sampling plan corresponds to a specified but relatively high probability of
acceptance.
3.14
limiting quality
LQ
〈sampling plan〉 quality level that corresponds to a specified and relatively low probability of acceptance
NOTE 1 It is the limiting lot quality characteristic that the consumer is willing to accept with a low probability that a lot of
this quality would occur.
NOTE 2 For the purposes of this International Standard, the limiting quality given in Table 11 corresponds to a
consumer's risk of 10 %.
3.15
self-locking torque
torque to be applied to the nut or bolt to maintain its movement of rotation in relation to the associated part,
the assembly being under no axial load and the nut-locking system being completely engaged with the bolt
(two pitches minimum protrusion including the end chamfer)
3.16
seating torque
tightening torque to be applied to the nut or bolt to introduce or to increase the axial load in the assembly
3.17
unseating torque
untightening torque to be applied to the nut or bolt to reduce or remove the axial load in the assembly

1) Ac = acceptance number (supplementary information taken from ISO 2859-1).
3.18
breakaway torque
torque required to start unscrewing the nut or bolt with respect to the associated part, with the nut-locking
device still fully engaged on the bolt, but after the axial load in the assembly has been removed by unscrewing
half a turn followed by a half in rotational movement
3.19
wrench torque
tightening and untightening torques which the driving feature of the nut shall withstand repeatedly, without any
permanent deformation which would prevent the appropriate wrench from being used and preclude re-use of
the nut
4 Quality assurance
4.1 General
The manufacturer shall be capable of continuous production of bolts complying with the quality requirements
specified in this International Standard. It is recommended that the manufacturer be certified to a recognized
quality management system. The certification authority may be the prime contractor.
The purpose of qualification inspections of nuts is to check that the design and manufacturing conditions of a
bolt allow it to satisfy the requirements of this International Standard.
Qualification of the bolts shall be granted by the Certification Authorities in the purchaser's country, or their
appointed representative, who may be the prime contractor.
The purpose of production acceptance inspection of a nut is to check, as simply as possible, using a method
which is inexpensive but the most representative of the actual conditions of use, with the uncertainty inherent
in statistical sampling, that the bolts satisfy the requirements of this International Standard.
Production acceptance inspections and tests shall be carried out by the manufacturer, or under his
responsibility.
4.2 Qualification inspection and test conditions
Qualification inspections and tests (requirements, methods, numbers of nuts) are specified in Table 1. They
shall be carried out on:
⎯ each type and diameter of nut;
⎯ 100 nuts selected from a single batch by simple random sampling.
The test programme may possibly be reduced, or qualification of a nut granted, without inspection or testing;
any such decision shall be based on the results obtained on similar types and diameters of nuts provided that
the design and manufacturing conditions are identical.
The inspections and tests shall be repeated on any nut if the supplier or the manufacturing conditions have
changed. Qualification inspections and tests are summarized in Table 2.
4.3 Production acceptance inspection and test conditions
Production acceptance inspections and tests (requirements, methods, numbers of nuts) are specified i
...