ISO 23886:2021

Overview

ISO 23886:2021 specifies a torque and preload test method for threaded, self-locking collars used in aerospace applications. The standard defines how to measure key performance parameters - locking torque, breakaway torque, torque off and preload - using calibrated torque/tension test benches or torsion machines. It was prepared by ISO/TC 20/SC 4 (Aerospace fastener systems) and includes procedural details, data processing and recommended test fixtures.

Key topics and technical requirements

• Scope and purpose: Test method for measuring torque and preload characteristics of threaded collars (self-locking).
• Test apparatus: Use a torque-tension test bench, torsion machine or equivalent precision equipment calibrated within 12 months.
• Test bolt: The bolt used with the collar must comply with the applicable product specification.
• Test accessories and interface:
  • Collar bearing surface material: alloy steel.
  • Surface roughness: Ra = 0.4 µm to 0.8 µm.
  • Hardness of contact washer: 50 HRC to 60 HRC.
• Test procedure (high level):
  • Install test bolt and collar; measure initial geometry and compute cycles.
  • Rotate collar at (10 ± 2) r/min until seating (hex portion twists off).
  • Release axial load, clamp unlocking area, reverse torque at (10 ± 2) r/min to measure disassembly behavior.
• Data capture and processing:
  • Record torque, tension and rotation angle to produce torque‑angle and tension‑angle curves.
  • From curves determine locking torque, preload, torque off and breakaway torque.
• Test reporting: Reports shall include part/lot/manufacturer, test machine model/serial/calibration date, measured torque/preload values and results.

Applications

• Aerospace fastener qualification: Verifying self-locking collar performance for aircraft and space vehicle assemblies where controlled preload and locking behavior are critical.
• Design validation: Engineers use the method to confirm design margins, friction behavior and seating characteristics of collars in structural and dynamic assemblies.
• Quality control and acceptance testing: Manufacturers and suppliers apply the procedure during production testing and lot acceptance to ensure consistent locking performance.
• Failure analysis: Test data (torque‑angle and tension‑angle curves) support investigations into unexpected loosening or seating issues.

Who should use this standard

• Aerospace fastener manufacturers and suppliers
• Mechanical and structural engineers working on bolted joints
• Test laboratories performing torque/preload characterization
• Quality and certification teams in aviation and space programs

Related standards

ISO 23886:2021 complements other aerospace fastener and torque/preload standards and should be used alongside applicable product specifications and industry fastener standards used by designers, procurement and test labs.