ISO 965-5:2025

Overview

ISO 965-5:2025 - ISO general purpose metric screw threads - Tolerances - Part 5 specifies limits of sizes and fundamental deviations for ISO metric internal threads (M) sized to mate with hot‑dip galvanized external threads. It applies to threads conforming to ISO 262 (M6 to M68 with coarse pitches and M72 to M100 with pitch 6) and to internal tolerance classes 6AZ and 6AX. The standard addresses pitch and minor diameters (and flank diameters via tables) for threads oversized to compensate for galvanizing thickness. It excludes internal threads that have a coating on the thread surface; limits before coating must be agreed between manufacturer and purchaser.

Key Topics

• Scope and applicability: Internal threads for general‑purpose metric screw threads to mate with hot‑dip galvanized external threads with maximum tolerance position h before galvanizing.
• Tolerance classes: Two internal classes - 6AZ (for thin galvanizing) and 6AX (for thicker galvanizing). 6AZ provides a smaller fundamental deviation; 6AX provides a larger deviation.
• Fundamental deviation formulas: The standard gives formulas for fundamental deviations as functions of pitch (P), with notes for small‑pitch exceptions.
• Limits of sizes: Detailed limit tables for pitch, flank diameters and minor diameters for both 6AZ and 6AX (tabulated for M6–M100 where applicable).
• Design and production rules: Threads must be manufactured after the hot‑dip galvanizing process (internal threads are not coated) and must conform to base/profile requirements of ISO 68‑1 and dimension selection per ISO 262.
• Assembly cautions: The document warns against assembling oversized internal threads (6AZ/6AX) with undersized external threads (6az) before galvanizing due to high risk of thread failure.

Applications and Who Uses It

• Fastener manufacturers specifying internal thread sizes to accommodate galvanizing.
• Galvanizing shops coordinating thread preparation and post‑galvanizing machining.
• Design and mechanical engineers ensuring reliable assemblies when external parts are hot‑dip galvanized.
• Quality inspectors and metrology labs verifying pitch and minor diameter limits against the ISO 965‑5 tables.
• Procurement and OEMs specifying thread classes (examples: M12 – 6AZ, M90 × 6 – 6AX) for supply contracts.

Practical benefits include controlled allowance for coating thickness, reduced risk of thread interference or stripping after galvanizing, and standardized designation for procurement and inspection.

Related Standards

• ISO 965-1 - Principles and fundamental data for metric thread tolerances
• ISO 965-4 - Limits for external threads to mate with internal threads after galvanizing
• ISO 68-1 - Basic and design profiles for metric threads
• ISO 262 - Selection of dimensions for fasteners
• ISO 5408 - Thread vocabulary

Keywords: ISO 965-5:2025, metric screw threads, tolerances, hot‑dip galvanized external threads, internal threads, 6AZ, 6AX, limits of sizes, pitch and minor diameters.