EN 3905:2008

Overview

EN 3905:2008 is a European standard developed by CEN that specifies the technical requirements and qualification criteria for six lobe recesses in bolts, particularly used in aerospace applications. This standard supplements the general bolt specifications by defining additional characteristics related to the six lobe recesses as detailed in EN 3911. The six lobe recess design, often recognized for its superior torque transmission and resistance to cam-out, is critical in aerospace fasteners where reliability and precision are paramount.

The standard was prepared by the Aerospace and Defence Industries Association of Europe (ASD-STAN) and mandates compliance across member countries, ensuring harmonization and quality assurance in aerospace bolting components.

Key Topics

• Scope and Applicability
  EN 3905:2008 covers the characteristics and qualification requirements of six lobe recesses on aerospace bolts. It applies in addition to the relevant bolt specifications currently in use.

• Geometrical Definition and Normative References
  The six lobe recess geometries conform to EN 3911, which outlines precise dimensional definitions. It also references ISO 5855-2 for thread limits applicable to bolts and nuts.

• Qualification and Testing Procedures
  The standard defines qualification testing focusing on the wrench feature test at ambient temperature. This involves torque application cycles to verify the mechanical integrity and wear resistance of the recess without permanent damage.

• Test Apparatus and Conditions
  Testing uses a hardened steel test block (minimum HRC 40) and a nut compliant with ISO 5855-2 threads. Lubrication with clean engine oil is specified to mirror operational conditions. Torque is applied alternately clockwise and counterclockwise for 15 cycles to ensure durability.

• Torque Values
  Specific wrench torque values are detailed in the standard, based on the bolt diameter, ensuring the bolts withstand operational stresses. These torque values relate to inducing approximately 75% of the yield strength (0.2% proof stress) for class 900 MPa bolts.

Applications

EN 3905:2008 is essential for manufacturers, engineers, and quality assurance professionals involved in:

• Aerospace Fastening Systems
  Ensuring fasteners with six lobe recesses meet stringent durability and performance requirements in aircraft and spacecraft assemblies.

• Defense and High-Reliability Equipment
  Applying established standards to maintain safety and operational integrity in defense aerospace components.

• Bolt Manufacturing and Certification
  Facilitating consistent production quality and compliance certification for bolts intended for aerospace use.

• Maintenance and Inspection Procedures
  Providing baseline testing methods for assessing the condition and serviceability of six lobe recess bolts during maintenance cycles.

Related Standards

• EN 3911 - Aerospace Series: Six Lobe Recess – Geometrical Definition
  Defines the geometry and dimensions of the six lobe recess critical to compliance with EN 3905:2008.

• ISO 5855-2 - Aerospace MJ Threads – Limit Dimensions for Bolts and Nuts
  Sets limits and thread requirements referenced for nuts used in testing the bolts covered by EN 3905:2008.

• Other Aerospace Bolt Specifications
  EN 3905 supplements various national and international bolt standards by focusing on the internal recess design rather than overall bolt dimensions or materials.

Keywords: EN 3905:2008, aerospace bolts, six lobe recess, technical specification, bolt qualification, aerospace fasteners, CEN standards, torque testing, aerospace series bolts, six lobe wrench, bolt testing, aerospace manufacturing, EN 3911, ISO 5855-2.