ISO 7720:2025

Overview

ISO 7720:2025 establishes the international standard for prevailing torque hexagon high nuts with slot(s) made entirely of metal. These fasteners are produced in steel and stainless steel, featuring metric coarse pitch threads ranging from M5 to M39. Designed as an enhancement of ISO 4032 and ISO 7042 specifications, this standard specifies nuts with an increased overall height to incorporate the prevailing torque feature with slots, thereby improving resistance and grip due to increased thread engagement.

The standard covers product grades A and B and emphasizes precise dimensional tolerances, functional requirements, mechanical properties, and marking protocols. The nuts aim to maintain reliable fastenings in diverse industrial applications where vibration resistance and secure locking are critical.

Key Topics

• Prevailing Torque Feature: All-metal hexagon high nuts with slots designed to provide a reliable locking function through friction torque, preventing loosening under vibration and dynamic loads.

• Dimensions and Tolerances: Includes detailed dimensional criteria for nuts from M5 to M39, with calculated heights (hmin, hmax) that vary systematically with diameter, deviating from the usual ISO tolerance code system to account for the special prevailing torque design.

• Material Specifications: Nuts are available in steel and stainless steel meeting product grades A and B. Selection of property classes and stainless-steel grades can reference ISO 898-2 and ISO 3506-2 respectively, ensuring mechanical performance aligned with customer requirements.

• Marking and Labeling: Clear marking on both the product and packaging is mandated to ensure traceability. Markings include thread size, property class, material grade, surface finish, manufacturer identification, and batch numbering, complying with ISO 898-2 and ISO 3506-2.

• Surface Treatments: Options for as-processed condition, electroplated, passivated coatings, and non-electrolytically applied zinc flake coatings are available per ISO 4042 and ISO 10683, enhancing corrosion resistance and performance.

• Reference Standards Integration: This standard aligns with relevant ISO norms such as ISO 965-1 for thread tolerances, ISO 4759-1 for fastener tolerances, and ISO 2320 for functional testing.

Applications

Prevailing torque hexagon high nuts with slots are particularly suited for:

• Mechanical assemblies subject to vibration and dynamic forces, such as automotive, aerospace, railroad, and heavy machinery sectors where reliable locking fasteners are critical.

• Corrosive environments, using stainless steel nut variants with proper property classes and grades to maximize corrosion resistance.

• Precision engineering, where specific torque retention and dimensional requirements guarantee operational safety and longevity.

• Construction and infrastructure, ensuring fasteners maintain preload in bolted joints over time despite environmental and mechanical stresses.

This standard supports engineers, quality assurance professionals, and manufacturers in selecting and specifying prevailing torque nuts that meet internationally recognized performance and safety criteria.

Related Standards

ISO 7720:2025 is closely linked with the following standards for comprehensive fastener specification and quality management:

• ISO 4032 - Hexagon regular nuts (style 1)
• ISO 7042 - Prevailing torque hexagon nuts (all metal)
• ISO 898-2 - Mechanical properties of carbon and alloy steel nuts
• ISO 3506-2 - Mechanical properties of stainless steel nuts
• ISO 965-1 - Basic screw thread tolerances
• ISO 4759-1 - Tolerances for bolts and nuts (product grades)
• ISO 2320 - Functional properties of prevailing torque nuts
• ISO 4042 and ISO 10683 - Coating systems for fasteners
• ISO 6157-2 - Surface discontinuity limits for nuts
• ISO 3269 - Acceptance inspection for fasteners

These standards collectively ensure the mechanical reliability, dimensional accuracy, and material performance of prevailing torque hexagon nuts, facilitating global interoperability and safety in critical fastening applications.

By adhering to ISO 7720:2025, industries ensure consistent quality and performance of prevailing torque hexagon high nuts with slots, reinforcing the integrity and safety of bolted assemblies worldwide.