SIST EN 3431:2008

Aerospace series - Nuts, hexagonal, self-locking, with counterbore and captive washer, in heat resisting steel, silver plated - Classification: 1 100 MPa (at ambient temperature) / 425 °C

This standard specifies the characteristics of self-locking hexagonal nuts, with counterbore and captive washer, in heat resisting steel, silver plated.
Classification: 1 100 MPa  ) / 425 °C  ).

Luft- und Raumfahrt - Sechskantmuttern, selbstsichernd, mit zylindrischer Aussenkung und Bördelscheibe, aus hochwarmfestem Stahl, versilbert - Klasse: 1 100 MPa (bei Raumtemperatur) / 425 °C

Diese Norm legt die Eigenschaften von selbstsichernden Sechskantmuttern mit zylindrischer Aussenkung und Bördelscheibe, aus hochwarmfestem Stahl, versilbert, fest.
Klasse: 1 100 MPa )/425 °C )

Série aérospatiale - Écrous hexagonaux, à freinage interne, avec chambrage et rondelle captive, en acier résistant à chaud, argentés - Classification : 1 100 MPa (à température ambiante) / 425 °C

Aeronavtika - Matice, šestrobe, samozapiralne, z ugreznjeno in robljeno podložko, iz toplotnoodpornega jekla, posrebrene - Klasifikacija: 1 100 MPa (pri temperaturi okolice) / 425 °C

General Information

• Status: Published
• Publication Date: 21-Jan-2008
• ICS: 49.030.30 - Nuts
• Technical Committee: I13 - Imaginarni 13
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 08-Jan-2008
• Due Date: 14-Mar-2008
• Completion Date: 22-Jan-2008
• Ref Project: EN 3431:2007 - Aerospace series - Nuts, hexagonal, self-locking, with counterbore and captive washer, in heat resisting steel, silver plated - Classification: 1 100 MPa (at ambient temperature) / 425 °C

Relations

• Revised: SIST EN 3531:2025 - Aerospace series - Steel X2NiCoMo18 8 5 (1.6359) - Vacuum induction melted and vacuum arc remelted - Solution treated and precipitation treated - Sheets and strips - a ≤ 6 mm - 1 750 MPa ≤ Rm ≤ 2 000 MPa
• Effective Date: 22-May-2024

Overview

SIST EN 3431:2008 is a European standard developed by CEN that specifies the characteristics and requirements for aerospace-grade self-locking hexagonal nuts. These nuts feature a counterbore and captive washer design, made from heat-resisting steel and silver plated for enhanced durability and corrosion resistance. SIST EN 3431:2008 classifies these nuts to withstand a minimum tensile stress of 1,100 MPa at ambient temperature and maintain their properties up to 425 °C.

The standard ensures consistency and safety in aerospace applications where high mechanical strength and resistance to extreme temperatures are critical. It is crucial for manufacturers, engineers, and quality assurance professionals working in the aerospace and defense industries.

Key Topics

• Material Specifications
  Nuts are manufactured using heat-resisting steel, designed for high-temperature stability. A silver plating is applied to improve corrosion resistance and surface protection following the guidelines of EN 2786 (electrolytic silver plating) and EN 2516 (passivation of corrosion-resistant steels).

• Design and Dimensions
  SIST EN 3431:2008 defines precise dimensions and tolerances based on ISO 8538 for hexagonal nuts with captive washers. Dimensions cover metric series MJ3 to MJ12 with detailed size, mass, and geometry parameters to ensure compatibility and interchangeability.

• Mechanical Performance
  Nuts must demonstrate a minimum tensile strength of 1,100 MPa at room temperature without cracking or deformation, even when paired with high-strength bolts. They are specified to withstand operational temperatures up to 425 °C without permanent alteration to their mechanical properties.

• Surface Treatments
  Silver plating thickness ranges from 5 to 15 micrometers, with stricter coverage requirements for nuts MJ6 and larger. Washers undergo passivation treatment to maintain corrosion resistance under high-temperature conditions.

• Quality and Compliance
  The standard requires manufacturers to adhere to aerospace quality management systems such as EN 9100 for production assurance and EN 9133 for product qualification. This ensures reliability and traceability throughout the manufacturing process.

• Marking and Identification
  Nuts are marked according to EN 2424 style N, including the standard number and diameter code for easy identification and compliance verification.

Applications

SIST EN 3431:2008 nuts are primarily designed for use in aerospace and defense industries where reliable fastening under extreme mechanical stress and temperature exposure is required. They are used in:

• Aircraft engine assemblies
• High-temperature aerospace components
• Structural aerospace fastenings requiring vibration resistance
• Defense equipment and space applications needing durable, heat-resistant fasteners
• Critical assemblies where self-locking features prevent loosening without additional locking devices

These nuts contribute significantly to operational safety, reliability, and maintenance efficiency in environments where tolerance to thermal cycling and mechanical fatigue is essential.

Related Standards

SIST EN 3431:2008 is referenced alongside several international and European aerospace standards to ensure comprehensive applicability and quality control:

• ISO 5855-2 – Defines limit dimensions for aerospace bolts and nuts.
• ISO 5858 – Procurement specifications for self-locking nuts with operating temperatures up to 425 °C.
• ISO 8538 – Dimension specifications for self-locking hexagonal nuts with captive washers in aerospace.
• ISO 8788 – Tolerances relating to form and position for metric aerospace nuts.
• EN 2424 – Requirements for marking aerospace products.
• EN 2516 – Passivation process for corrosion-resistant steels.
• EN 2786 – Electrolytic silver plating guidelines for fasteners.
• EN 9100 – Aerospace quality management systems based on ISO 9001.
• EN 9133 – Qualification procedures for aerospace standard parts.
• TR 3791 – Guidance on materials for self-locking nuts and inserts operating at temperatures ≤ 425 °C.

Summary

SIST EN 3431:2008 sets a rigorous framework for self-locking hexagonal nuts used in high-temperature aerospace applications. With detailed requirements on materials, design, mechanical properties, and quality management, this standard ensures that fasteners meet the demanding conditions found in modern aircraft and defense systems. Adhering to SIST EN 3431:2008 guarantees compatibility, safety, and durability for critical aerospace components where reliability is paramount.

Keywords: EN 3431, aerospace nuts, self-locking hexagonal nuts, captive washer, heat resisting steel, silver plated nuts, aerospace fasteners, high temperature nuts, aerospace standards, CEN aerospace standard, tensile strength 1100 MPa, temperature resistance 425 °C, aerospace quality management

Standards Content (Sample)

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Aerospace series - Nuts, hexagonal, self-locking, with counterbore and captive washer, in heat resisting steel, silver plated - Classification: 1 100 MPa (at ambient temperature) / 425 °CAeronavtika - Matice, šestrobe, samozapiralne, z ugreznjeno in robljeno podložko, iz toplotnoodpornega jekla, posrebrene - Klasifikacija: 1 100 MPa (pri temperaturi okolice) / 425 °CSérie aérospatiale - Écrous hexagonaux, à freinage interne, avec chambrage et rondelle captive, en acier résistant à chaud, argentés - Classification : 1 100 MPa (à température ambiante) / 425 °CLuft- und Raumfahrt - Sechskantmuttern, selbstsichernd, mit zylindrischer Aussenkung und Bördelscheibe, aus hochwarmfestem Stahl, versilbert - Klasse: 1 100 MPa (bei Raumtemperatur) / 425 °CTa slovenski standard je istoveten z:EN 3431:2007SIST EN 3431:2008en49.030.30ICS:SLOVENSKI
STANDARDSIST EN 3431:200801-marec-2008

EUROPEAN STANDARD NORME EUROPÉENNE EUROPÄISCHE NORM
EN 3431
December 2007 ICS 49.030.30 English Version
Aerospace series - Nuts, hexagonal, self-locking, with counterbore and captive washer, in heat resisting steel, silver plated - Classification: 1 100 MPa (at ambient temperature) / 425 °C
Série aérospatiale - Écrous hexagonaux, à freinage interne, avec chambrage et rondelle captive, en acier résistant à chaud, argentés - Classification : 1 100 MPa (à température ambiante) / 425 °C
Luft- und Raumfahrt - Sechskantmuttern, selbstsichernd, mit zylindrischer Aussenkung und Bördelscheibe, aus hochwarmfestem Stahl, versilbert - Klasse: 1 100 MPa (bei Raumtemperatur) / 425 °C This European Standard was approved by CEN on 5 November 2007.
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. Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the CEN Management Centre or to any CEN member.
This European Standard exists 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 Management Centre has the same status as the official versions.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: rue de Stassart, 36
B-1050 Brussels © 2007 CEN All rights of exploitation in any form and by any means reserved worldwide for CEN national Members. Ref. No. EN 3431:2007: E
...