EN ISO 3506-4:2025 PDF

Overview

EN ISO 3506-4:2025 - “Fasteners - Mechanical properties of corrosion‑resistant stainless steel fasteners - Part 4: Tapping screws with specified grades and hardness classes (ISO 3506-4:2025)” - is a CEN-adopted international standard that defines mechanical and physical property requirements for corrosion‑resistant stainless steel tapping screws. It covers tapping screws manufactured from austenitic, martensitic, ferritic and duplex stainless steels, with specified stainless steel grades and hardness classes, and applies to threads ST2,2 to ST8 (per ISO 1478). The standard clarifies operational temperature guidance (tests at ambient 10 °C–35 °C; intended use −20 °C to +150 °C) and excludes tapping screws with special properties (e.g., weldability).

Key topics and technical requirements

• Material coverage: austenitic, martensitic, ferritic and duplex stainless steels; chemical composition and heat‑treatment considerations are specified where applicable.
• Designation system: structured identification of stainless steel grades and hardness classes for tapping screws.
• Hardness and strength: requirements for surface and core hardness, including specific hardness classes (note: austenitic grade A8 and duplex grades D2–D8 were added for hardness classes 20H, 25H and 30H).
• Functional tests: mandated test methods include hardness testing (surface and core), torsional strength tests and drive (forming) tests to verify thread‑forming ability and performance.
• Inspection and conformity: manufacturer’s, supplier’s and purchaser’s inspection provisions; delivery of test results and marking/labeling requirements are included.
• Corrosion and surface condition: requirements and improved guidance on surface finish, coatings and corrosion resistance; magnetic properties are also addressed.
• Scope limits: testing is performed at ambient temperatures (10 °C–35 °C), and the user is responsible for verifying suitability outside the stated service range.

Practical applications and users

Who benefits from EN ISO 3506-4:2025:

• Fastener manufacturers specifying stainless steel grades, hardness classes, and test regimes for tapping screws.
• Design and specification engineers in construction, metal fabrication, electronics, HVAC and other industries where corrosion resistance and tapping screw performance are critical.
• Procurement and quality assurance teams requiring standardized marking, labelling and inspection records to ensure product conformity.
• Test laboratories implementing the hardness, torsional and drive tests defined by the standard.

Use cases:

• Specifying tapping screws for assemblies exposed to corrosive environments where mechanical reliability and standardized material identification are required.
• Creating supplier contracts and acceptance criteria that reference harmonized mechanical property and testing rules.

Related standards

• ISO 1478 - thread sizes ST2,2 to ST8 referenced for tapping screws.
• ISO 3506-6 - provides general rules and additional technical information on stainless steel grades (corrosion behaviour, detailed properties, magnetic properties) intended to be used together with this Part 4.

Keywords: EN ISO 3506-4:2025, stainless steel tapping screws standard, corrosion‑resistant fasteners, hardness classes, mechanical properties, ISO 1478, tapping screw tests.