Overview
EN ISO 7720:2025 - Fasteners: Prevailing torque hexagon nuts - High nuts (all metal) with slot(s) - specifies the characteristics, dimensions and functional requirements for all‑metal prevailing‑torque hexagon high nuts with slot(s). It covers steel and stainless‑steel nuts with metric coarse‑pitch threads from M5 to M39, and defines product grades A and B. The standard clarifies design rules (notably increased nut height to accommodate the prevailing‑torque feature) and adds marking and labelling requirements.
Key topics and technical requirements
- Scope & geometry: High hexagon nuts with slot(s) designed to provide prevailing torque; overall height h is greater than ISO 7042 to allow for the locking feature and increased engaged threads. mmin follows ISO 4032. Note: the tolerance (hmax − hmin) does not follow the ISO IT tolerance system.
- Thread sizes & product grades: Metric coarse pitch threads M5–M39. Product grade A for D ≤ M16 (with specific M5 adjustment), product grade B for D > M16.
- Materials & mechanical properties: Steel and stainless‑steel options; property classes and heat‑treatment rules referenced to ISO 898‑2 (steel) and ISO 3506‑2 (stainless steel).
- Functional performance: Prevailing torque characteristics and functional properties are linked to ISO 2320.
- Tolerances & dimensions: Thread tolerance class 6H by default (6G may be specified for coated nuts); dimensional rules and tables for d, s, h, m, w as given in the standard.
- Surface, coatings & finish: As‑processed, electroplated coatings (ISO 4042), zinc‑flake (ISO 10683), passivation and lubrication options - to be agreed between purchaser and supplier.
- Inspection & marking: Acceptance inspection per ISO 3269, surface discontinuities per ISO 6157‑2, and marking/labelling requirements (Clause 6).
Applications and practical value
- Ensures consistent locking performance for assemblies where vibration resistance and reuse are required (automotive, rail, heavy machinery, industrial equipment, marine).
- Useful for designers and engineers specifying locking nuts for safety‑critical joints.
- Provides procurement and quality teams with harmonized acceptance, testing and marking rules to streamline supply chain compliance.
- Manufacturers use the standard to design and produce nuts with predictable torque/locking behaviour and defined mechanical properties.
Who should use this standard
- Fastener manufacturers and product designers
- Mechanical engineers and OEMs (automotive, construction, machinery, marine)
- Quality/inspection personnel and procurement/specification writers
Related standards
ISO 4032, ISO 7042, ISO 898‑2, ISO 3506‑2, ISO 2320, ISO 965‑1, ISO 4759‑1, ISO 4042, ISO 10683, ISO 3269, ISO 6157‑2, ISO 8991/8992
Keywords: EN ISO 7720:2025, prevailing torque hexagon nuts, high nuts (all metal), slot(s), metric coarse pitch thread, product grade A, product grade B, fasteners standard.