ISO 965-5:1998

Overview

ISO 965-5:1998 is an international standard published by the International Organization for Standardization (ISO) that defines the tolerances and limits of sizes for internal metric screw threads designed to mate with hot-dip galvanized external screw threads. Specifically, it addresses internal threads conforming to ISO 262 with the basic profile specified in ISO 68-1, which are matched with external screw threads having a maximum tolerance position h before galvanizing.

This part of the ISO 965 series provides detailed specifications for pitch diameter and crest diameter deviations for internal screw threads to ensure proper fit and mechanical performance after the galvanizing process, considering the dimensional changes caused by the protective zinc coating.

Key Topics

• Scope and Application
  ISO 965-5 defines deviations and limits of sizes for internal metric threads intended to mate with hot-dip galvanized external threads that have tolerance position h at their maximum size before galvanizing. This is vital as hot-dip galvanizing increases the external thread diameter due to zinc coating thickness.

• Tolerance Classes
  The standard specifies two primary tolerance classes for internal threads:

  • 6AZ: For mating with centrifuged external threads after galvanizing, ensuring tight fit and reduced risk of interference.
  • 6AX: Intended for mating with heavily coated, non-centrifuged hot-dip galvanized external threads, accommodating thicker zinc layers.

• Fundamental Deviations
  The fundamental deviations for internal threads are calculated using formulas based on pitch (P) in millimeters and expressed in micrometers (µm):

  • For AZ: EI_AZ = + (300 + 20P) µm
  • For AX: EI_AX = + (220P - 20) µm
    These calculations adjust dimensions to accommodate the galvanizing process effects on external threads.

• Limits of Sizes
  The standard provides detailed tables of dimensional limits for major diameter, pitch diameter, and minor diameter of threads across various sizes (e.g., M10 to M64) for both 6AZ and 6AX classes. These limits are essential for manufacturers and quality control to ensure compatibility and functional performance.

• Compatibility Warning
  ISO 965-5 strongly advises against mating internal threads adhering to its tolerances with external threads specified in ISO 965-4, due to the risk of thread stripping caused by incompatible tolerance classes.

• Mechanical Properties
  Products manufactured according to this standard might exhibit load failure during testing as per ISO 898-2 unless other mechanical properties are adjusted accordingly.

Applications

• Hot-Dip Galvanized Fastening Systems
  ISO 965-5 is primarily applied in industries where metric fasteners undergo hot-dip galvanizing for corrosion protection, including construction, automotive, machinery manufacturing, and infrastructure.

• Quality Control and Inspection
  Manufacturing processes depend on the precise limits and tolerances defined by ISO 965-5 to ensure proper thread engagement, mechanical strength, and prevention of failure in fastened joints after galvanizing.

• Thread Design and Engineering
  Engineers designing components involving galvanized screw threads use ISO 965-5 to specify internal threading dimensions that will reliably mate with coated external threads, optimizing for durability and fit.

• Maintenance and Replacement Parts
  Standardized thread tolerances help maintenance teams select compatible replacement parts for galvanized assemblies, reducing risks of mismatches or mechanical failures.

Related Standards

• ISO 68-1: Defines the basic profile for ISO general purpose screw threads, which ISO 965-5 threads conform to.
• ISO 262: Lists selected sizes for metric screw threads, bolts, and nuts that serve as the basis for thread design in ISO 965-5.
• ISO 965-1: Provides the general principles and basic data for screw thread tolerances upon which ISO 965-5’s tolerance qualities are derived.
• ISO 965-4: Specifies limits for sizes of hot-dip galvanized external threads to mate with internal threads tapped with tolerance position H or G after galvanizing. ISO 965-5 explicitly cautions against combining internal threads per its guidelines with external threads specified in this part.
• ISO 898-2: Describes mechanical properties and proof load values of nuts, relevant for testing products manufactured according to ISO 965-5.
• ISO 5408: Standard vocabulary related to cylindrical screw threads, used to ensure consistent terminology.

Keywords: ISO 965-5, metric screw threads, internal screw threads, hot-dip galvanizing, thread tolerances, pitch diameter limits, screw thread deviations, thread design, galvanized fasteners, ISO metric threads, screw thread standards, tolerance classes 6AZ and 6AX, mechanical properties of fasteners.