Overview
ISO 965-2:2024 specifies the limits of sizes for internal and external ISO general purpose metric screw threads (M) - focusing on pitch and crest/major/minor diameters for standardized metric fastening threads. It applies to threads conforming to ISO 262 with basic and design profiles per ISO 68-1 and covers tolerance classes 6H/6g for M1.6 to M100 and 5H/6h for M1 to M1.4. This fourth edition updates size coverage (adds large diameters up to M100) and length-of-engagement data for selected sizes.
Key topics and requirements
- Scope of dimensions: Limits of sizes given for pitch diameter and crest/root diameters of internal (nuts, tapped holes) and external (bolts, studs) threads.
- Tolerance classes covered:
- Internal: 5H (≤ M1.4), 6H (> M1.4)
- External: 6h (≤ M1.4), 6g (> M1.4)
- Tolerance quality and engagement: Medium tolerance quality; normal length group of thread engagement is used for tabulated limits.
- Tables of limits: Numeric limits for each nominal diameter/pitch and length-of-engagement are provided (see Tables 1 & 2 in the standard).
- Coated threads: Tolerances apply to parts before coating unless otherwise stated; after coating the thread profile must not exceed the maximum material limit for H/h tolerance positions. The GO thread plug or ring gauge requirement after coating is specified for thin coatings.
- Reference design rules: Root contours, truncations and fundamental deviations derive from ISO 965-1; designation per ISO 965-1.
Practical applications
Who uses ISO 965-2 and why:
- Design engineers - to specify thread size and tolerance limits ensuring interchangeability and assembly fit.
- Fastener manufacturers & machinists - to set production tolerances and verify parts against standard limits.
- Quality/inspection labs - to select and use GO/NO-GO gauges and perform dimensional inspection of pitch and crest diameters.
- Procurement/spec writers - to reference correct tolerance classes for procurement and contract specifications.
- Coating/process engineers - to ensure plated threads meet post-coating gauge and fit requirements.
Practical uses include specifying thread fits for assemblies, defining acceptance criteria for bolts/nuts, selecting gauge sizes, and ensuring reliable interchangeability in mechanical systems.
Related standards
- ISO 965-1 - Principles and basic data for metric thread tolerances
- 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 965-2, metric screw threads, thread tolerances, limits of sizes, internal threads, external threads, tolerance classes 6H 6g 5H 6h, M1.6 to M100, GO/NO-GO gauges.
Open preview (PDF)ISO general purpose metric screw threads — Tolerances — Part 2: Limits of sizes for internal and external threads (tolerance classes 6H and 6g for M1,6 to M100 and 5H and 6h for M1 to M1,4)