SIST EN 4634:2009

Overview

SIST EN 4634:2009 specifies the requirements and characteristics for aerospace screws with a 100° countersunk head, six lobe recess, and short thread, manufactured in heat resisting steel FE-PA2601 (A286), and passivated for enhanced corrosion resistance. This standard is integral to the aerospace sector, defining mechanical fastening components that meet demanding criteria for high strength and performance at elevated temperatures - up to 900 MPa (ambient) and service temperatures to 650 °C.

Companies and engineers in the aerospace industry rely on this European standard to ensure consistency, safety, and compatibility of mechanical fasteners used in critical structural and engine applications.

Key Topics

• Screw Design Features
  • 100° countersunk head for flush mounting and optimized aerodynamics
  • Six lobe recess (also known as Torx®-type), enabling higher torque transmission and reduced risk of cam-out during installation
  • Short-thread specification for specific assembly requirements
• Material and Processing
  • Manufactured from FE-PA2601 (A286) heat resisting steel, ensuring high tensile strength and stability at high temperatures
  • Passivated surface treatment, delivering corrosion protection suitable for harsh aerospace environments
• Dimensional and Quality Criteria
  • Detailed requirements for configuration, dimensions, form tolerances, and marking practices
  • Reference to key European and ISO standards for thread types (MJ threads according to ISO 5855-2), tolerances (ISO 7913), and geometrical features (EN 3911)
• Mechanical Classification
  • Classified for 900 MPa minimum tensile strength at ambient temperature and operational capability up to 650 °C

Applications

Screws covered by SIST EN 4634:2009 are utilized in a range of aerospace applications where high-temperature strength, reliability, and corrosion resistance are critical, including:

• Aircraft structure fastening: Securing panels, skins, and access doors where smooth, flush installation is necessary for aerodynamics
• Engine and turbine assemblies: Withstanding thermal stresses and mechanical loads in propulsion systems
• Avionics and electronic mounting: Providing robust, vibration-resistant fastening in sensitive equipment
• Spacecraft and satellite components: Confidence in performance despite temperature extremes and vacuum conditions

The six lobe recess design is particularly valued in maintenance environments for easier installation and reduced tool wear, while the material’s elevated temperature capacity aligns with current aerospace engineering demands.

Related Standards

For a comprehensive approach to the design, selection, and use of aerospace fasteners, the following standards are referenced within SIST EN 4634:2009 or offer relevant guidance:

• ISO 5855-2: Aerospace MJ threads - Limit dimensions for bolts and nuts
• ISO 7913: Tolerances of form and position for bolts and screws in aerospace applications
• EN 2399: Heat resisting steel FE-PA2601 technical specification for material properties
• EN 2516: Passivation of corrosion resisting steels and decontamination of nickel base alloys
• EN 3911: Six lobe recess - Geometrical definition for aerospace fasteners
• EN 2576: Bolts in heat resisting steel technical specifications

Using SIST EN 4634:2009 ensures that aerospace fasteners are engineered for durability, safety, and compatibility with international aerospace requirements, supporting optimal aircraft design and maintenance operations.

Keywords: aerospace screws, 100° countersunk head, six lobe recess, FE-PA2601, A286 steel, passivated fasteners, high temperature screws, MJ thread, European aerospace standard, EN 4634, aerospace fasteners.