SIST EN 3843:2011

Overview

SIST EN 3843:2011 is a European standard developed by CEN that specifies the characteristics of bihexagonal self-locking nuts with a counterbore. These nuts are manufactured from heat-resisting steel and are passivated to enhance corrosion resistance. Designed specifically for aerospace applications, this standard ensures that the nuts can withstand a tensile stress of 1100 MPa at ambient temperature and maintain structural integrity at temperatures up to 650 °C.

This aerospace series standard is critical in defining the mechanical, dimensional, and material requirements for these specialized nuts used in high-temperature environments, typical of aerospace and defense industry components.

Key Topics

• Bihexagonal Configuration
  The nuts have a bihexagonal shape compliant with ISO 4095, optimizing wrench engagement and torque transfer.

• Self-Locking Feature
  The self-locking mechanism is achieved by a controlled out-of-round deformation of the nut’s thread area, providing reliable locking performance under vibration and thermal cycling.

• Material and Surface Treatment
  Made from heat-resisting steel, these nuts are passivated according to EN 2516, which improves corrosion resistance in demanding aerospace environments.

• Mechanical Classification
  The nuts are classified to withstand a minimum tensile stress of 1100 MPa at ambient temperature and perform effectively up to 650 °C without permanent deformation or loss of mechanical properties.

• Dimensional and Tolerance Requirements
  Detailed dimensional specifications including thread codes, mass approximations, and form tolerances follow ISO 5855-2 and ISO 8788 to ensure uniformity and interchangeability.

• Marking and Identification
  Marking is standardized by EN 2424:2008 style N, facilitating traceability and quality assurance in aerospace manufacturing and maintenance.

• Quality Management and Product Qualification
  Manufacturers must comply with EN 9100 Quality Management Systems specific to aviation, space, and defense organizations, and products must undergo qualification according to EN 9133 procedures.

Applications

EN 3843 nuts are essential components in aerospace manufacturing and maintenance where high performance under mechanical stress and elevated temperature is required. Common practical applications include:

• Aircraft Engine Assemblies
  Components exposed to extreme heat and vibration, where secure fastening is critical.

• Spacecraft and Satellite Construction
  Structural fastening requiring high tensile strength and resistance to thermal extremes.

• Defense Equipment
  High-strength locking nuts for military aerospace vehicles and weapons systems requiring reliable operation under demanding conditions.

• High-Temperature Industrial Use
  Specialized aerospace hardware applicable in industrial turbines and heat-critical machinery.

These nuts provide reliable fastening solutions that maintain mechanical integrity, locking ability, and corrosion resistance, directly supporting safety, performance, and durability in aerospace systems.

Related Standards

• EN 2424:2008 – Marking of aerospace products, ensuring consistent identification practices.
• EN 2516 – Passivation of corrosion-resistant steels and decontamination of nickel base alloys, defining surface treatment processes.
• EN 9100 – Quality management requirements for aviation, space, and defense organizations.
• EN 9133 – Qualification procedures for aerospace standard parts, covering product approval.
• ISO 4095 – Specifications for bihexagonal drives and wrenching configurations in metric series.
• ISO 5855-2 – Limits and dimensions for aerospace bolts and nuts, providing dimensional tolerance standards.
• ISO 8641 – Procurement specifications for self-locking nuts with maximum operating temperatures exceeding 425 °C.
• ISO 8788 – Tolerances of form and position for aerospace metric nuts.
• TR 3791 – Technical report on materials for self-locking nuts and inserts at temperature classes up to 425 °C.

Together, these standards complement SIST EN 3843:2011 by providing comprehensive guidelines on material selection, manufacturing, testing, quality management, and product handling for aerospace fasteners.

Keywords: EN 3843, aerospace nuts, bihexagonal self-locking nuts, heat resistant steel nuts, passivated nuts, aerospace fasteners, high temperature nuts, mechanical fastening aerospace, self-locking nuts classification, aerospace industry standards.