Overview
ISO 7719:2025 is an international standard that defines the specifications for prevailing torque hexagon nuts-regular nuts made entirely of metal. This standard applies to steel and stainless steel nuts with metric coarse pitch threads ranging from M5 to M39. It covers product grades A and B, establishing detailed dimensions, mechanical properties, and marking and labelling requirements to ensure consistent quality and performance.
The nuts specified in ISO 7719:2025 are designed with an overall height equal to the minimum height defined in ISO 898-2 and ISO 4032 (style 1) plus the prevailing torque feature. This prevailing torque aspect ensures that the nuts maintain a locking function through metal-to-metal friction, providing secure fastening without additional locking elements.
Key Topics
- Dimensions and Tolerances: Design dimensions for nuts from M5 to M39 are precisely specified, including parameters such as thread pitch, hex dimensions, and nut heights. Tolerances apply differently than standard ISO tolerances due to the prevailing torque feature.
- Material and Property Classes: Covers steel and stainless steel nuts with guidance on selecting property classes and stainless steel grades per ISO 898-2 (carbon/alloy steel) and ISO 3506-2 (corrosion-resistant stainless steel). Property classes influence mechanical performance and durability.
- Functional Requirements: Addresses mechanical and functional properties, ensuring prevailing torque nuts perform reliably under load. It acknowledges the lack of an international test method for stainless steel nuts and encourages consultation of national standards.
- Marking and Labelling: Specifies clear markings on nuts and labelling on packaging, including reference to ISO 7719, thread size, material grades, property classes, surface finishes, manufacturer info, and lot numbers to facilitate traceability and quality control.
- Surface Finishes and Coatings: Covers requirements for as-processed, bright, passivated, lubricated, and coated finishes including electroplated and non-electrolytic zinc flake coatings, essential for corrosion resistance and performance.
Applications
ISO 7719 prevailing torque hexagon nuts are critical components in industries and applications requiring reliable fastening under vibration, thermal cycling, or dynamic loads. Common uses include:
- Mechanical and Structural Engineering: Secure fastening in machines, frames, and assemblies.
- Automotive and Transportation: Components subjected to vibration and movement where self-locking nuts improve safety.
- Construction and Infrastructure: Fastening structural elements with high resistance to loosening.
- Corrosive Environments: Stainless steel nuts per ISO 3506-2 provide increased corrosion resistance for marine, chemical, or outdoor applications.
- Manufacturing and Assembly Lines: Standardized nuts enable interchangeability and consistent quality across mass production.
Related Standards
ISO 7719:2025 references several key international standards to maintain comprehensive quality and compatibility:
- ISO 898-2: Mechanical properties and property classes for steel nuts.
- ISO 3506-2: Mechanical properties and grades for stainless steel nuts.
- ISO 4032: Hexagon regular nuts, style 1 dimensions.
- ISO 965-1: Tolerances for metric screw threads.
- ISO 2320: Prevailing torque steel nuts - functional properties.
- ISO 4759-1: Tolerances for fasteners including nuts.
- ISO 4042 and ISO 10683: Coating and surface treatment standards.
- ISO 6157-2: Surface discontinuities acceptance criteria.
- ISO 3269: Inspection and acceptance of fasteners.
By adhering to ISO 7719:2025, manufacturers, engineers, and quality professionals ensure the production and use of high-performance prevailing torque hexagon nuts that conform to globally recognized dimensions, mechanical properties, and quality standards-ensuring safety, reliability, and consistency across various industrial applications.