oSIST prEN 3299:2026

• Abstract:

  This document specifies the characteristics, qualification and acceptance requirements for self-locking shaft-nuts and threaded rings, with right- or left-hand MJ threads, in FE-PA2601, silver-plated, for aerospace applications.; Temperature class: 450 °C .; It is applicable whenever referenced.

• Status: Not Published
• Public Enquiry End Date: 09-Oct-2026
• ICS: 49.030.30 - Nuts
• ICS: 49.030.50 - Washers and other locking elements
• Technical Committee: I13 - Imaginarni 13
• Current Stage: 4020 - Public enquire (PE) (Adopted Project)
• Start Date: 12-Aug-2026
• Due Date: 30-Dec-2026
• Ref Project: prEN 3299 - Aerospace series - Shaft-nut and threaded ring, self-locking, right- or left-hand MJ threads, in heat resisting steel FE-PA2601 (A286), silver plated - Technical specification

• Revises: SIST EN 3299:2019 - Aerospace series - Shaft-nuts and threaded rings, self-locking, right- or left-hand MJ threads, in heat resisting steel FE-PA2601 (A286), silver plated - Technical specification
• Effective Date: 11-Mar-2026

prEN 3299:2026 is a draft European Standard prepared by ASD-STAN and published through CEN. It specifies the characteristics, qualification and acceptance requirements for self-locking shaft-nuts and threaded rings with right- or left-hand MJ threads, made from heat resisting steel FE-PA2601 (A286) and silver plated for aerospace applications. The standard covers parts in temperature class 450 °C and is applicable whenever referenced.

What does oSIST prEN 3299:2026 specify?

oSIST prEN 3299:2026 sets the technical specification for a defined family of aerospace fasteners: self-locking shaft-nuts and threaded rings with MJ threads, in FE-PA2601 (A286), silver plated. It tells users what the parts must be like, how they are qualified, and how batches are accepted for supply.

The document is organized into Scope, Normative references, Terms and definitions, Quality assurance, Requirements, and three normative annexes. Clause 4 covers qualification and acceptance, while Clause 5 gives the product requirements and test methods.

Annex	What it covers
Annex A	Checking bearing surface perpendicularity
Annex B	Method of checking locking torque
Annex C	Hardness test

What are the key requirements of oSIST prEN 3299:2026?

Quality assurance and sampling

Clause 4.1 requires qualification inspections and tests on each type and diameter of nut or ring, plus 12 items selected from one batch by simple random sampling. In practice, qualification is type-specific and sample-based, so a supplier must show performance on representative parts before release.

Clause 4.1.2 requires the manufacturer to be an approved production organization for aerospace products and to maintain a quality management system such as EN 9100 or an equivalent aerospace-accepted system. That matters because the standard ties product approval to the manufacturer's controlled process, not just to final inspection.

Clause 4.2 requires acceptance inspections and tests on each batch, with parts selected by simple random sampling. Acceptance is the routine batch release step, and Clause 4.2.4 says a test report with actual numerical values shall be provided if the purchase order asks for it.

Product characteristics and manufacture

Clause 5.1 requires material conformity to the product standard or definition document, and Clause 5.2 requires dimensions and tolerances of form and position to match the same controlling document. For buyers and inspectors, this means the ordering document must define the exact part variant and geometry limits.

Clause 5.3.1 requires the nuts or rings to be manufactured by machining and sets the heat-treatment sequence. It also limits contamination from the heat-treatment medium and requires scale removal without harming dimensions, surface finish or mechanical properties.

Clause 5.3.2 covers bearing surface perpendicularity, with the detailed check given in Annex A. Clause 5.3.3 allows thread deformation in the locking area, but the part still has to pass the go-thread check before the locking element engages, so the functional thread fit must be verified before deformation.

Clause 5.3.4 requires surface roughness to follow ISO 21920-3 and the product standard or definition document. Clause 5.3.5 covers the silver coating by reference to EN 2786 and then splits the checks into appearance, thickness and adhesion, which means the coating is not only decorative but also a controlled product characteristic.

Functional, mechanical and metallurgical checks

Clause 5.4.1 requires reusability testing, with self-locking torque and seating/unseating torque measured through repeated cycles. Annex B gives the torque method, including the ambient-temperature cycle and the 450 °C baking cycle, so the user can verify that the locking feature still works after thermal exposure and repeated assembly.

Clause 5.4.2 requires hardness within the stated range, measured according to Annex C. Clause 5.5 then adds metallurgical checks: a predominantly recrystallized microstructure, grain size limits by ASTM E112, no cracks, limited seams, limited oxide penetration, and material identification by non-destructive test.

Clauses 5.6 to 5.8 cover product identification, packaging and labelling. In practice, these clauses support traceability and handling control by requiring marking, individual packing to prevent damage or corrosion, and labels that state the designation, quantity, batch number, and manufacturer identification.

What terms does oSIST prEN 3299:2026 define?

• Finished nut or ring - A nut or ring ready for use, including any treatments and surface coatings required by the product standard or definition document.
• Definition document - The document that states all requirements for finished nuts or rings.
• Batch - A quantity of finished nuts or rings of the same type and diameter, from the same material melt, made in the same production cycle and route, with the same heat and surface treatments.
• Production cycle - The period during which production continues without any voluntary or unforeseen change in manufacturing parameters.
• Self-locking torque - The torque needed to keep the nut or ring rotating relative to the associated part when there is no axial load and the locking zone is fully engaged.
• Breakaway torque - The torque needed to start unscrewing the nut or ring after the axial load has been removed by half a turn and rotation has been stopped.
• Apparent seating torque - The torque indicated by the wrench during tightening.
• Effective seating torque - The part of the apparent seating torque that actually introduces or increases axial load in the assembly.

Who uses oSIST prEN 3299:2026?

oSIST prEN 3299:2026 is used by aerospace fastener manufacturers, quality assurance teams, test laboratories, and purchasing or specification engineers. It is also relevant to organizations that approve production, qualify parts, and release batches for aerospace use.

In practice, these users apply it when selecting the correct nut or ring, defining the purchase requirement, setting up qualification testing, checking coating and hardness, and verifying batch acceptance. It is the reference that links design intent, process control, and inspection for this specific fastener family.

What changed in oSIST prEN 3299:2026 from the previous edition?

oSIST prEN 3299:2026 supersedes EN 3299:2019. The foreword states one significant technical change: the process in Table 3 for surface discontinuities was updated.

Which standards are used with oSIST prEN 3299:2026?

Standard	What it contributes
EN 2786	Requirements for electrolytic silver plating of fasteners
EN ISO 6507-1	Vickers hardness test method
EN ISO 6508-1	Rockwell hardness test method
EN ISO 3452-1	Penetrant testing principles for surface discontinuities
ISO 21920-3:2021	Surface texture profile specification operators for roughness control
ISO 5855-2	Limit dimensions for MJ thread gauges used in the torque and fit checks
ASTM E112	Method for determining average grain size
EN 9100	Example of an aerospace quality management system for manufacturer approval
EN 9133	Qualification procedure for aerospace standard products
ISO 3534-2:2006	Source for the definition of simple random sampling

What does the oSIST prEN 3299:2026 document contain?

The document contains a requirement table that links each characteristic to its test method and identifies whether it is for qualification or acceptance. It also contains a sample-allocation table for qualification and a sampling plan for acceptance, which helps users decide how many parts to test and which checks apply to each sample group.

Annex A gives the inspection device and procedure for bearing surface perpendicularity. Annex B gives the locking-torque test method and the torque values by thread size and test condition. Annex C gives the hardness test method, the permitted test methods, and the permitted test areas on the part.

The document also includes a figure for the inspection device and tables for thread-related checking dimensions and torque conditions. These parts are used for conformity testing, batch release, and qualification of the part design and manufacturing process.

SLOVENSKI STANDARD
01-oktober-2026
Aeronavtika - Gredna matica in navojni obroč, samozapiralni, levi ali desni navoj
MJ, iz toplotnoodpornega jekla FE-PA2601 (A286), posrebreni - Tehnična
specifikacija
Aerospace series - Shaft-nut and threaded ring, self-locking, right- or left-hand MJ
threads, in heat resisting steel FE-PA2601 (A286), silver plated - Technical specification
Luft- und Raumfahrt - Wellenmutter und Gewindering, selbstsichernd, Rechts- oder
Links-MJ-Gewinde, aus hochwarmfestem Stahl FE-PA2601 (A286), versilbert -
Technische Lieferbedingung
Série aérospatiale - Écrous d’arbres et bagues filetées, à freinage interne, filetage MJ à
droite ou à gauche, en acier résistant à chaud FE-PA2601 (A286), argentés -
Spécification technique
Ta slovenski standard je istoveten z: prEN 3299
ICS:
49.030.30 Matice Nuts
49.030.50 Podložke in drugi blokirni Washers and other locking
elementi elements
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

DRAFT
EUROPEAN STANDARD
NORME EUROPÉENNE
EUROPÄISCHE NORM
July 2026
ICS 49.030.50; 49.030.30 Will supersede EN 3299:2019
English Version
Aerospace series - Shaft-nut and threaded ring, self-
locking, right- or left-hand MJ threads, in heat resisting
steel FE-PA2601 (A286), silver plated - Technical
specification
Série aérospatiale - Écrous d'arbres et bagues filetées, Luft- und Raumfahrt - Wellenmutter und Gewindering,
à freinage interne, filetage MJ à droite ou à gauche, en selbstsichernd, Rechts- oder Links-MJ-Gewinde, aus
acier résistant à chaud FE-PA2601 (A286), argentés - hochwarmfestem Stahl FE-PA2601 (A286), versilbert -
Spécification technique Technische Lieferbedingung
This draft European Standard is submitted to CEN members for enquiry. It has been drawn up by the Technical Committee ASD-
STAN.
If this draft becomes a European Standard, CEN members are bound to comply with the CEN/CENELEC Internal Regulations
which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.

This draft European Standard was established by CEN in three official versions (English, French, German). A version in any other
language made by translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC
Management Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and
United Kingdom.
Recipients of this draft are invited to submit, with their comments, notification of any relevant patent rights of which they are
aware and to provide supporting documentation.

Warning : This document is not a European Standard. It is distributed for review and comments. It is subject to change without
notice and shall not be referred to as a European Standard.

EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2026 CEN All rights of exploitation in any form and by any means reserved Ref. No. prEN 3299:2026 E
worldwide for CEN national Members.

Contents Page
European foreword . 3
1 Scope . 4
2 Normative references . 4
3 Terms and definitions . 4
4 Quality assurance . 6
4.1 Qualification . 6
4.1.1 General. 6
4.1.2 Approval of manufacturers . 6
4.1.3 Qualification of screws . 7
4.2 Acceptance. 7
4.2.1 Purpose . 7
4.2.2 Conditions . 7
4.2.3 Responsibility . 7
4.2.4 Inspection and test report . 7
5 Requirements . 7
Annex A (normative) Checking bearing surface perpendicularity . 15
Annex B (normative) Method of checking locking torque . 18
Annex C (normative) Hardness test . 21
Bibliography . 23

European foreword
This document (prEN 3299:2026) has been prepared by ASD-STAN.
After enquiries and votes carried out in accordance with the rules of this Association, this document has
received the approval of the National Associations and the Official Services of the member countries of
ASD-STAN, prior to its presentation to CEN.
This document is currently submitted to the CEN Enquiry.
This document will supersede EN 3299:2019.
— Table 3, surface discontinuities process updated.
1 Scope
This document specifies the characteristics, qualification and acceptance requirements for self-locking
shaft-nuts and threaded rings, with right- or left-hand MJ threads, in FE-PA2601, silver-plated, for
aerospace applications.
Temperature class: 450 °C .
It is applicable whenever referenced.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements 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.
EN 2786, Aerospace series - Electrolytic silver plating of fasteners
EN ISO 6507-1, Metallic materials - Vickers hardness test - Part 1: Test method (ISO 6507-1)
EN ISO 6508-1, Metallic materials - Rockwell hardness test - Part 1: Test method (ISO 6508-1)
EN ISO 3452-1, Non-destructive testing - Penetrant testing - Part 1: General principles (ISO 3452-1)
ISO 21920-3:2021, Geometrical product specifications (GPS) — Surface texture: Profile — Part 3:
Specification operators
ISO 5855-2, Aerospace — MJ threads — Part 2: Limit dimensions for bolts and nuts
ASTM E112, Standard Test Methods for Determining Average Grain Size
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https://www.iso.org/obp
— IEC Electropedia: available at https://www.electropedia.org/
3.1
finished nut or ring
nut or ring ready for use, inclusive of any possible treatments and/or surface coatings, as specified in the
product standard or definition document
3.2
definition document
document specifying all the requirements for finished nuts or rings

Maximum test temperature of the parts.
Published by American Society for Testing and Materials (ASTM), available at: https://www.astm.org/.
3.3
batch
quantity of finished nuts or rings, of the same type and same diameter, produced from the same 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
production cycle
period during which production proceeds without any voluntary or unforeseen change in manufacturing
parameters
3.5
heat treatment cycle
period during which the oven continuously remains at nominal treatment temperature
3.6
surface treatment cycle
period during which the surface treatment proceeds without any voluntary or unforeseen change in
surface treatment parameters
3.7
surface discontinuities
—
3.7.1
crack
rupture in the material which may extend in any direction and which may be intercrystalline or
transcrystalline in character
3.7.2
seam
open surface discontinuity
3.7.3
lap
surface discontinuity caused by folding over metal fins or sharp corners
3.7.4
inclusions
non-metallic particles originating from the material manufacturing process
Note 1 to entry: These particles may be isolated or arranged in strings.
3.8
sampling plan
plan according to which one or more samples are taken in order to obtain information and possibly reach
a decision
3.9
simple random sampling
taking 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
[SOURCE: ISO 3534-2:2006, 1.3.4, modified – “sampling where a sample of n sampling units” deleted;
“unit” replaced with “item”]
3.10
self-locking torque
torque to be applied to the nut or ring to maintain its movement of rotation in relation to the associated
part, the assembly being under no axial load and the locking zone being completely engaged on the
associated part (minimum protrusion of two pitches, including the end chamfer)
3.11
breakaway torque
torque required to start unscrewing the nut or ring with respect to the associated part, with the locking
zone still fully engaged, but after the axial load in the assembly has been removed by unscrewing half a
turn followed by a halt in rotational movement
3.12
effective seating torque
part of the apparent seating torque which introduces or increases the axial load in the assembly; the
effective seating torque is equal to the difference between the apparent seating torque and the self-
locking torque
3.13
apparent seating torque
torque indicated by the dynamometric wrench when tightening
4 Quality assurance
4.1 Qualification
4.1.1 General
See EN 9133.
Qualification inspections and tests (requirements, methods, numbers of nuts or rings) are specified in
Table 1. They shall be carried out on
— each type and diameter of nut or ring and
— 12 nuts or rings selected from a single batch by simple random sampling.
The test programme may possibly be reduced or the qualification be granted without inspection or
testing: any such decision shall be based on the results obtained on similar diameters of nuts or rings,
provided that the design and manufacturing conditions are identical.
Table 2 indicates the allocation of nut or ring samples for the inspections and tests.
4.1.2 Approval of manufacturers
The manufacturer’s operations shall be an approved production organization for aerospace products and
shall demonstrate that it has implemented and is able to maintain a quality management system (e.g. in
accordance with EN 9100 or an equivalent aerospace accepted and established quality management
system).
4.1.3 Qualification of screws
The qualification procedure for aerospace standard products (e.g. in accordance with EN 9133 or an
equivalent aerospace accepted and established qualification procedure) shall be used and documented
in accordance with the specified tests if not otherwise agreed between customer and supplier.
4.2 Acceptance
4.2.1 Purpose
The purpose of acceptance inspections and tests is to check, as simply as possible, by a method
representative of actual use conditions, with the uncertainty inherent to statistical sampling, that the nuts
or rings constituting the batch satisfy the requirements of this document.
4.2.2 Conditions
Acceptance inspections and tests (requirements, methods, numbers of nuts or rings) are specified in
Table 1. They shall be carried out on each batch. Nuts or rings from the batch to be tested shall be selected
by simple random sampling.
Each nut or ring may be submitted to several inspections or tests.
If a more stringent inspection is deemed necessary, all or part of the qualification inspections and tests
may be performed during the acceptance inspection and testing. In this case, the sample submitted to
these inspections and tests is the same as that submitted for qualification inspection and tests.
4.2.3 Responsibility
Acceptance inspections and tests shall be carried out by the manufacturer, or under his responsibility.
4.2.4 Inspection and test report
A test report showing actual numerical values shall be provided if specified in the purchase order.
5 Requirements
Requirements shall be in accordance with Table 1.
Table 1 — Technical requirements and test methods
Clause Characteristic Requirement Inspection and Q/A Sample
test method a size
5.1  Material In accordance with the Chemical analysis Q
product standard or or certificate of
A
definition document. compliance issued
by the
manufacturer of
the semi-finished
product
5.2  Dimensions, In accordance with the Standard gauging Q 9
tolerances of product standard or
A Table 3
form and definition document.
position
Clause Characteristic Requirement Inspection and Q/A Sample
test method a size
5.3  Manufacturing The nuts or rings shall be Examination of the Q
manufactured by machining. manufacturing

process
The heat treatment medium Examination of the
5.3.1  Heat treatment Q
or atmosphere shall not heat treatment

cause any surface equipment
contamination except as
permitted by 5.5.4.
Solution treat (if applicable) Examination of the Q
at a temperature of 900 °C heat treatment

to 980 °C held at the
process
selected temperature
within ± 15 °C for between
1 h min. and 2 h max.
quench in oil, or alternative
medium or faster.
Precipitation treat at
(720 ± 10) °C held at
temperature for
16 h −0 +30 min cooled in
air or faster process.
Any scale shall be removed Visual examination
by mechanical or chemical
processes. It shall not
deteriorate the dimensions,
surface finish and
mechanical properties of the
parts. In particular, it shall
not result in embrittlement
of the metallic substrate.
5.3.2  Bearing In accordance with the In accordance with Q 3
surface per- product standard or Annex A.
pendicularity definition document.
A Table 3
...