EN ISO 7040:2025 PDF

Overview - EN ISO 7040:2025 (Fasteners, prevailing torque hexagon nuts)

EN ISO 7040:2025 specifies the characteristics of prevailing-torque hexagon regular nuts with a non‑metallic insert (commonly nylon/polyamide) in steel and stainless steel, covering metric coarse‑pitch threads from M3 to M39. It defines dimensions, product grades, material options and key functional requirements for regular hex nuts that provide a prevailing (self‑locking) torque. The standard updates and supersedes EN ISO 7040:2012 and aligns with ISO technical requirements for fasteners.

Key topics and technical requirements

• Size and dimensions: Detailed dimension tables for M5–M39; Annex A covers nuts with D < M5 (e.g., M3, M4) designed to style 1 principles.
• Prevailing‑torque feature: Nuts are designed with overall height = mmin (ISO 898-2 / ISO 4032 style 1) plus the prevailing‑torque feature. The insert height (hmax – mmin) is identical across regular, high and thin nuts for a given diameter. Shape of the prevailing feature is at the manufacturer’s discretion (max diameter ≤ s).
• Materials and grades: Steel and stainless steel options. Property classes for steel are taken from ISO 898‑2; stainless steel grades from ISO 3506‑2. Product grades: A for D ≤ M16 (with specific note for D ≤ M5) and B for D > M16.
• Thread and tolerances: Metric coarse pitch threads with tolerance class 6H and references to ISO 965‑1 for thread tolerances.
• Functional and acceptance requirements: Functional properties reference ISO 2320 (prevailing torque behavior); acceptance and inspection guidance refer to ISO 3269 and ISO 6157‑2. Surface treatments and coatings are covered by ISO 4042 and ISO 10683 where applicable.
• Marking and labelling: Clause 6 adds requirements for product marking and package labelling to support traceability.

Practical applications and users

EN ISO 7040:2025 is intended for:

• Fastener manufacturers specifying and producing non‑metallic‑insert prevailing torque hex nuts
• Design and mechanical engineers selecting locking nuts for machinery, automotive, rail, construction, and equipment assemblies
• Procurement and quality inspectors verifying compliance, marking and acceptance testing
• Maintenance and service teams requiring standardized self‑locking nuts for reliable re‑assembly

Benefits: ensured interchangeability, predictable locking torque behavior, and compatibility with international mechanical property and corrosion‑resistance classes.

Related standards

• ISO 898‑2 (mechanical properties of nuts)
• ISO 3506‑2 (stainless steel fasteners)
• ISO 2320 (prevailing torque functional properties)
• ISO 965‑1 (metric thread tolerances)
• ISO 4759‑1, ISO 4042, ISO 10683, ISO 3269, ISO 6157‑2, ISO 8992

Keywords: EN ISO 7040:2025, prevailing torque hexagon nuts, non‑metallic insert, fasteners, metric nuts M3–M39, ISO 7040, product grade A/B, ISO 898‑2, ISO 3506‑2.