ISO 3506-3:2025

Overview

ISO 3506-3:2025 - "Fasteners - Mechanical properties of corrosion resistant stainless steel fasteners - Part 3: Set screws" specifies the mechanical and physical properties of set screws and similar headless fasteners not subjected to tensile stress. It covers austenitic and duplex stainless steels, defined grades and hardness classes, designation and marking, inspection and test methods, and limits for use. Key operational notes: testing is performed at ambient 10 °C to 35 °C and intended service range is –20 °C to +150 °C; users must verify suitability outside these limits.

Key topics and technical requirements

• Scope and limits
  • Applies to ISO metric threaded set screws with nominal diameters 1.6 mm to 24 mm, thread geometries per ISO 68-1, ISO 261, ISO 262, and tolerances per ISO 965-1 / ISO 965-2.
  • Excludes screws under tensile stress (see ISO 3506-1) and does not set requirements for shear strength or weldability.
• Designation system
  • Two-block identification: stainless steel grade (A = austenitic, D = duplex) and hardness class (e.g., “-21H”); low-carbon variants may use “L”.
• Materials and properties
  • Chemical composition, surface condition (finish/coating), corrosion resistance and magnetic behaviour are addressed; detailed metallurgical guidance referenced in ISO 3506-6.
• Mechanical requirements
  • Hardness classes and acceptable ranges are defined; hardness testing follows international methods (Brinell, Vickers, Rockwell - ISO 6506-1, ISO 6507-1, ISO 6508-1).
  • Proof torque requirements and test procedures are specified for socket set screws.
• Inspection, testing and marking
  • Manufacturer, supplier and purchaser inspection clauses; delivery of test results and labelling requirements. Test document types per ISO 16228 and vocabulary referencing ISO 1891-4.

Applications and users

ISO 3506-3 is intended for:

• Fastener manufacturers and heat-treatment providers who must certify grades and hardness classes of stainless set screws.
• Design and mechanical engineers specifying corrosion-resistant fasteners for assemblies where screws are loaded in compression (not tension).
• Quality/inspection teams and procurement specialists verifying supplier claims and test reports.
• Industries using corrosion-resistant hardware (e.g., marine, chemical processing, machinery, oil & gas), where stainless set screws are chosen for corrosion resistance and specific hardness.

Related standards

• ISO 3506-1 (screws under tensile stress)
• ISO 3506-6 (general rules and stainless steel selection)
• ISO 68-1, ISO 261, ISO 262, ISO 965-1 / ISO 965-2 (metric threads & tolerances)
• ISO 6506-1, ISO 6507-1, ISO 6508-1 (hardness test methods)
• ISO 16228, ISO 1891-4

Using ISO 3506-3 helps ensure consistent specification, testing and traceability of corrosion resistant stainless steel set screws, supporting reliable engineering selections and supplier verification.