ISO 3506-3:2009

Overview

ISO 3506-3:2009 defines the mechanical properties of corrosion‑resistant austenitic stainless steel set screws and similar fasteners not under tensile stress. It applies to nominal thread diameters 1.6 mm ≤ d ≤ 24 mm, triangular ISO metric threads (per ISO 68‑1, ISO 261, ISO 262) and covers testing at ambient temperatures of 10 °C to 35 °C. The standard classifies fasteners into hardness classes, specifies marking/finish guidance and references test methods for hardness and proof torque.

Keywords: ISO 3506-3:2009, stainless steel fasteners, set screws, mechanical properties, hardness classes, proof torque, austenitic stainless steel

Key topics and requirements

• Scope and applicability: Set screws and similar non‑tensioned fasteners (any shape) made from austenitic stainless steel within the stated diameter and thread types. Excludes screws with special properties (e.g., weldability).
• Designation system: Two‑block marking - steel grade (A = austenitic, e.g., A2, A4) and hardness class (e.g., 12H, 21H). Low‑carbon grades can be marked with “L”; passivated items may carry “P” (e.g., A4-21HP).
• Hardness classes: Minimum Vickers hardness values are defined: 12H = HV ≥ 125, 21H = HV ≥ 210. Equivalent Brinell and Rockwell ranges are specified.
• Proof torque: Hexagon socket set screws have minimum proof torque requirements given in tabulated form by nominal diameter and point type (flat, cone, dog, cup). Table 3 in the standard provides the specific minima.
• Chemical composition: Acceptable austenitic steel grades and composition ranges are listed (see Table 2). Recommendations for low‑carbon or stabilized grades where intergranular corrosion may be a concern.
• Testing methods: Proof torque test for hexagon socket set screws (clause 6.1) and hardness tests (HB, HRB, HV per clause 6.2), referencing ISO 6506‑1, ISO 6507‑1 and ISO 6508‑1.
• Marking, finish and passivation: Guidance on manufacturer identification, package labeling and optional passivation per ISO 16048.

Applications and users

ISO 3506-3 is used by:

• Fastener manufacturers for product specification, production control and marking
• Design and mechanical engineers selecting set screws for assemblies
• Quality and test laboratories performing hardness and torque verification
• Procurement and inspection teams ensuring purchased fasteners meet mechanical requirements
• Industries requiring corrosion‑resistant hardware (machinery, instrumentation, marine and chemical process equipment)

Practical value: ensures consistent mechanical performance, traceability (grade/hardness marking), and fit‑for‑purpose selection of stainless steel set screws.

Related standards

• ISO 3506 (Parts 1, 2, 4) - other stainless fastener types
• ISO 68‑1, ISO 261, ISO 262 - metric thread profiles and sizes
• ISO 6506‑1, ISO 6507‑1, ISO 6508‑1 - hardness test methods
• ISO 16048 - passivation of stainless steel fasteners
• ISO 3651‑1 / ISO 3651‑2 - intergranular corrosion tests
• ISO 16426 - fastener quality assurance

For specification or procurement, reference ISO 3506-3:2009 alongside the relevant product and test standards to ensure compliance with mechanical and corrosion‑resistance requirements.