ISO 965-4:2025

Overview

ISO 965-4:2025 defines the limits of sizes and fundamental deviations for hot‑dip galvanized metric external threads intended to mate with internal threads made to tolerance position H or G after galvanizing. It applies to external metric threads (M) conforming to ISO 262 with basic/design profiles per ISO 68-1 - specifically M6 to M68 (coarse pitches) and M72 to M100 (pitch 6). The standard covers threads that are undersized to tolerance class 6az before galvanizing so that, after zinc coating, they correctly fit internal threads at H or G positions.

Key topics and requirements

• Scope and applicability: External threads undersized to 6az before galvanizing to mate with internal threads in tolerance positions H or G after galvanizing.
• Fundamental deviations: The fundamental deviation for tolerance position az is specified (see Table 1). The deviation is calculated using the formula given in the standard:
  es = −(300 + 20·P) (values in micrometres; not applicable for pitch P < 1 mm).
• Limits of sizes: Table 2 lists maximum and minimum major and pitch diameters for the 6az class across the covered nominal diameters and pitches; these limits are derived from the fundamental deviation and the tolerances in ISO 965-1.
• Tolerance quality and class: Specified as medium quality, normal length of engagement, tolerance class 6az (applied prior to galvanizing).
• Design and profile: Root contours and truncations follow ISO 965-1; basic and design profiles per ISO 68-1.
• Restrictions: External 6az threads must not be mated with internal threads oversized to 6AZ or 6AX (see Clause 4) due to high risk of thread stripping.
• Designation examples: M12 – 6az; M90 × 6 – 6az.

Applications and users

ISO 965-4:2025 is intended for professionals who specify, manufacture, inspect or procure hot‑dip galvanized threaded fasteners and components, including:

• Mechanical and structural designers engineering bolted joints where galvanizing is required
• Fastener manufacturers and thread rolling/tapping tool designers
• Galvanizing service providers coordinating pre‑galvanizing thread allowances
• Quality assurance and inspection teams verifying post‑coating thread fit
• Procurement and standards engineers specifying compliant thread classes

Typical use cases include structural steelwork, infrastructure, utility mounting hardware and other assemblies where hot‑dip galvanizing is applied and reliable thread engagement after coating is critical.

Related standards

• ISO 965-1 - Principles and basic data for metric screw thread tolerances
• ISO 965-5 - Limits for internal threads to mate with galvanized external threads
• ISO 68-1 - Basic and design profiles for metric screw threads
• ISO 262 - Selected sizes for bolts, screws, studs and nuts
• ISO 5408 - Screw threads vocabulary

Keywords: ISO 965-4:2025, hot-dip galvanized external threads, metric screw threads, tolerance class 6az, tolerance position H, tolerance position G, limits of sizes, fundamental deviations.