ISO 965 Metric Thread Tolerance Classes
The ISO 965 tolerance system for general-purpose metric threads, current editions: designation notation, controlled diameters with grades and positions, fundamental deviations, grade multipliers, grade-6 tolerance widths and calculated 6g/6H limits M3 - M64 — the current-edition companion to the legacy BS 3643 tabulations in this family.
Last updated: 2026-11
Specifications
This collected page tabulates the current ISO 965 system the way modern drawings reference it. It opens with the designation grammar (M20 × 2.5 - 6H: internal, grade 6, position H; 6H/6g as a mating pair), then the controlled-diameter map (internal threads: grades 4-8 at positions G/H on pitch and minor diameters; external: grades 3-9 at e/f/g/h on pitch diameter, 4/6/8 on major), the fundamental-deviation formulas (EI for G = +(15 + 11P) µm; es for g = −(15 + 11P) µm, with the small-pitch exceptions noted) and the es-for-g numeric ladder (−20.5 at P 0.5 to −81.0 at P 6.0 µm). The grade structure follows: multipliers relative to grade 6 (0.50 at grade 3 to 2.00 at grade 9 on external pitch diameter; 0.63/1.00/1.60 on major), and the grade-6 widths per thread — T d2 (6) 78 µm at M3 × 0.5 rising to 279 at M64 × 6, with the internal T D2, external T d and internal T D1 companions per size. The calculated-limits table then assembles it all: external 6g d/d2 min/max and internal 6H D1/D2 min/max per size M3 - M64 (M12 × 1.75 external: d 11.707/11.966, d2 10.681/10.829; internal: D1 10.106/10.446, D2 10.863/11.059), closing with a worked M20 × 2.5 example shown before ISO table rounding. Where this page stops — classes beyond the 6g/6H defaults, the fine selections beyond M64 — the legacy BS 3643 machinery page in this family carries the class matrices and worked examples; the full 6g/6H limits ladder to M300 sits on the BS 3643 limits page. Strength and torque are per RFQ.
| Designation system | Size × pitch - class notation; 6H/6g as the general-purpose mating pair; examples carried verbatim |
|---|---|
| Controlled diameters | Internal D2/D1: grades 4-8, positions G/H; external d2: grades 3-9, positions e/f/g/h; external d: grades 4/6/8 |
| Deviations | Formulas per position (P in mm) + es-for-g ladder −20.5 to −81.0 µm, P 0.5 - 6.0 |
| Grades | Multipliers 0.50 - 2.00 vs grade 6 (external pitch dia); grade-6 widths T d2/T D2/T d/T D1 per thread M3 - M64 |
| Calculated 6g/6H limits | M3 - M64: external d/d2 min-max, internal D1/D2 min-max, mm to three decimals |
| Not tabulated | Classes beyond the tabulated defaults, sizes above M64 (see BS 3643 pages), hot galvanized overrides, strength — per RFQ |
| Standard | Purpose |
|---|---|
| ISO 68-1:2023 | Basic and design profiles for ISO metric screw threads. |
| ISO 261:1998 | General plan for ISO general-purpose metric screw threads. |
| ISO 262:2023 | Selected metric thread sizes for bolts, screws, studs and nuts. |
| ISO 724:2023 | Basic dimensions for ISO general-purpose metric screw threads. |
| ISO 965-1:2026 | Principles and basic data for the ISO metric thread tolerance system. |
| ISO 965-2:2024 | Limits of size for 6H/6g fastening threads M1.6 to M100 and 5H/6h M1 to M1.4. |
| ISO 965-3:2021 | Limit deviations for recommended ISO metric thread tolerance classes. |
| Example | Meaning |
|---|---|
| M20 × 2.5 - 6H | M20 internal thread, 2.5 mm pitch, tolerance grade 6 at position H. |
| M20 × 2.5 - 6g | M20 external thread, 2.5 mm pitch, tolerance grade 6 at position g. |
| M20 × 2.5 - 6H/6g | Mating internal 6H and external 6g threads. |
| Thread | Controlled diameter | Common tolerance grades | Tolerance positions |
|---|---|---|---|
| Internal | Pitch diameter D 2 | 4, 5, 6, 7, 8 | G, H |
| Internal | Minor diameter D 1 | 4, 5, 6, 7, 8 | G, H |
| External | Pitch diameter d 2 | 3, 4, 5, 6, 7, 8, 9 | e, f, g, h |
| External | Major diameter d | 4, 6, 8 | e, f, g, h |
| Thread | Position | Fundamental deviation |
|---|---|---|
| Internal | G | EI = +(15 + 11P) µm |
| Internal | H | EI = 0 |
| External | e | es = −(50 + 11P) µm, subject to small-pitch exceptions |
| External | f | es = −(30 + 11P) µm, subject to small-pitch exceptions |
| External | g | es = −(15 + 11P) µm |
| External | h | es = 0 |
| Pitch P (mm) | es for g (µm) | Pitch P (mm) | es for g (µm) |
|---|---|---|---|
| 0.5 | −20.5 | 2.0 | −37.0 |
| 0.7 | −22.7 | 2.5 | −42.5 |
| 0.8 | −23.8 | 3.0 | −48.0 |
| 1.0 | −26.0 | 3.5 | −53.5 |
| 1.25 | −28.8 | 4.0 | −59.0 |
| 1.5 | −31.5 | 4.5 | −64.5 |
| 1.75 | −34.3 | 5.0 | −70.0 |
| 5.5 | −75.5 | 6.0 | −81.0 |
| Controlled diameter | Grade | Multiplier relative to grade 6 |
|---|---|---|
| External pitch diameter d 2 | 3 | 0.50 |
| External pitch diameter d 2 | 4 | 0.63 |
| External pitch diameter d 2 | 5 | 0.80 |
| External pitch diameter d 2 | 6 | 1.00 |
| External pitch diameter d 2 | 7 | 1.25 |
| External pitch diameter d 2 | 8 | 1.60 |
| External pitch diameter d 2 | 9 | 2.00 |
| External major diameter d | 4 / 6 / 8 | 0.63 / 1.00 / 1.60 |
| Internal minor diameter D 1 | 4 / 5 / 6 / 7 / 8 | 0.63 / 0.80 / 1.00 / 1.25 / 1.60 |
| Thread | Basic pitch dia. d 2 = D 2 (mm) | Basic internal minor dia. D 1 (mm) | g deviation es (µm) | T d2 (6) (µm) | T D2 (6) (µm) | T d (6) (µm) | T D1 (6) (µm) |
|---|---|---|---|---|---|---|---|
| M3 × 0.5 | 2.675 | 2.459 | -20 | 78 | 103 | 109 | 135 |
| M4 × 0.7 | 3.545 | 3.242 | -23 | 90 | 118 | 138 | 180 |
| M5 × 0.8 | 4.480 | 4.134 | -24 | 94 | 125 | 152 | 202 |
| M6 × 1 | 5.350 | 4.917 | -26 | 111 | 146 | 177 | 230 |
| M8 × 1.25 | 7.188 | 6.647 | -29 | 121 | 160 | 206 | 269 |
| M10 × 1.5 | 9.026 | 8.376 | -32 | 130 | 172 | 233 | 305 |
| M12 × 1.75 | 10.863 | 10.106 | -34 | 148 | 196 | 259 | 340 |
| M14 × 2 | 12.701 | 11.835 | -37 | 157 | 207 | 284 | 374 |
| M16 × 2 | 14.701 | 13.835 | -37 | 157 | 207 | 284 | 374 |
| M18 × 2.5 | 16.376 | 15.294 | -42 | 171 | 226 | 330 | 437 |
| M20 × 2.5 | 18.376 | 17.294 | -42 | 171 | 226 | 330 | 437 |
| M22 × 2.5 | 20.376 | 19.294 | -42 | 171 | 226 | 330 | 437 |
| M24 × 3 | 22.051 | 20.752 | -48 | 197 | 261 | 373 | 496 |
| M27 × 3 | 25.051 | 23.752 | -48 | 197 | 261 | 373 | 496 |
| M30 × 3.5 | 27.727 | 26.211 | -54 | 210 | 277 | 413 | 553 |
| M33 × 3.5 | 30.727 | 29.211 | -54 | 210 | 277 | 413 | 553 |
| M36 × 4 | 33.402 | 31.670 | -59 | 221 | 292 | 452 | 607 |
| M39 × 4 | 36.402 | 34.670 | -59 | 221 | 292 | 452 | 607 |
| M42 × 4.5 | 39.077 | 37.129 | -64 | 232 | 306 | 489 | 659 |
| M45 × 4.5 | 42.077 | 40.129 | -64 | 232 | 306 | 489 | 659 |
| M48 × 5 | 44.752 | 42.587 | -70 | 260 | 343 | 525 | 710 |
| M52 × 5 | 48.752 | 46.587 | -70 | 260 | 343 | 525 | 710 |
| M56 × 5.5 | 52.428 | 50.046 | -76 | 270 | 356 | 560 | 759 |
| M60 × 5.5 | 56.428 | 54.046 | -76 | 270 | 356 | 560 | 759 |
| M64 × 6 | 60.103 | 57.505 | -81 | 279 | 369 | 593 | 806 |
| Thread | External thread 6g – calculated limits (mm) | Internal thread 6H – calculated limits (mm) | ||||||
|---|---|---|---|---|---|---|---|---|
| d min | d max | d 2 min | d 2 max | D 1 min | D 1 max | D 2 min | D 2 max | |
| M3 × 0.5 | 2.871 | 2.979 | 2.576 | 2.655 | 2.459 | 2.594 | 2.675 | 2.779 |
| M4 × 0.7 | 3.839 | 3.977 | 3.433 | 3.523 | 3.242 | 3.422 | 3.545 | 3.664 |
| M5 × 0.8 | 4.825 | 4.976 | 4.362 | 4.457 | 4.134 | 4.336 | 4.480 | 4.605 |
| M6 × 1 | 5.797 | 5.974 | 5.214 | 5.324 | 4.917 | 5.147 | 5.350 | 5.497 |
| M8 × 1.25 | 7.765 | 7.971 | 7.038 | 7.159 | 6.647 | 6.916 | 7.188 | 7.348 |
| M10 × 1.5 | 9.735 | 9.969 | 8.864 | 8.994 | 8.376 | 8.682 | 9.026 | 9.198 |
| M12 × 1.75 | 11.707 | 11.966 | 10.681 | 10.829 | 10.106 | 10.446 | 10.863 | 11.059 |
| M14 × 2 | 13.679 | 13.963 | 12.507 | 12.664 | 11.835 | 12.209 | 12.701 | 12.908 |
| M16 × 2 | 15.679 | 15.963 | 14.507 | 14.664 | 13.835 | 14.209 | 14.701 | 14.908 |
| M18 × 2.5 | 17.628 | 17.957 | 16.163 | 16.334 | 15.294 | 15.730 | 16.376 | 16.602 |
| M20 × 2.5 | 19.628 | 19.957 | 18.163 | 18.334 | 17.294 | 17.730 | 18.376 | 18.602 |
| M22 × 2.5 | 21.628 | 21.957 | 20.163 | 20.334 | 19.294 | 19.730 | 20.376 | 20.602 |
| M24 × 3 | 23.579 | 23.952 | 21.806 | 22.003 | 20.752 | 21.249 | 22.051 | 22.312 |
| M27 × 3 | 26.579 | 26.952 | 24.806 | 25.003 | 23.752 | 24.249 | 25.051 | 25.312 |
| M30 × 3.5 | 29.533 | 29.947 | 27.463 | 27.673 | 26.211 | 26.764 | 27.727 | 28.004 |
| M33 × 3.5 | 32.533 | 32.947 | 30.463 | 30.673 | 29.211 | 29.764 | 30.727 | 31.004 |
| M36 × 4 | 35.489 | 35.941 | 33.121 | 33.343 | 31.670 | 32.277 | 33.402 | 33.694 |
| M39 × 4 | 38.489 | 38.941 | 36.121 | 36.343 | 34.670 | 35.277 | 36.402 | 36.694 |
| M42 × 4.5 | 41.446 | 41.935 | 38.781 | 39.013 | 37.129 | 37.788 | 39.077 | 39.384 |
| M45 × 4.5 | 44.446 | 44.935 | 41.781 | 42.013 | 40.129 | 40.788 | 42.077 | 42.384 |
| M48 × 5 | 47.405 | 47.930 | 44.423 | 44.682 | 42.587 | 43.297 | 44.752 | 45.095 |
| M52 × 5 | 51.405 | 51.930 | 48.423 | 48.682 | 46.587 | 47.297 | 48.752 | 49.095 |
| M56 × 5.5 | 55.365 | 55.925 | 52.083 | 52.352 | 50.046 | 50.805 | 52.428 | 52.784 |
| M60 × 5.5 | 59.365 | 59.925 | 56.083 | 56.352 | 54.046 | 54.805 | 56.428 | 56.784 |
| M64 × 6 | 63.326 | 63.919 | 59.743 | 60.022 | 57.505 | 58.311 | 60.103 | 60.471 |
| Feature | Calculated result before ISO table rounding |
|---|---|
| External major diameter d | 19.628 to 19.958 mm |
| External pitch diameter d 2 | 18.163 to 18.334 mm |
| Internal minor diameter D 1 | 17.294 to 17.731 mm |
| Internal pitch diameter D 2 | 18.376 to 18.602 mm |
Materials
- Thread class interacts with finish: the 6g external clearance is what a standard zinc plating eats into, while hot-dip galvanized threads need a larger allowance (a class shift or an oversized-tapped nut) — that is a specification decision to make at RFQ, not on the stockroom floor. Order by size, pitch and class; when plating is in the specification, state it, and we quote the thread class that survives the coating build
Ordering & documentation
Documents
Shipments are backed by Mill Test Certificate (MTC), Dimensional Report, Salt Spray Test Report on request, with full batch traceability from raw material to finished product. Quality management follows the owner-confirmed compliance list: ISO 9001:2015, RoHS, REACH. Exact document sets are confirmed on the order.
Quotation
- The fastener family (ISO 965 Metric Thread Tolerance Classes) plus the standard designation from your drawing — DIN / ISO / JIS / ASTM / ANSI, or a drawing for custom parts.
- Size (diameter and length), thread type (metric or inch), property class or grade, and coating or finish.
- Quantity per size and your target delivery date.
- Destination country, and any required documents (for example a mill test certificate) so the quote includes them.
Sample & supply
Minimum order quantity is 10,000 pieces. Stock items run 3–7 days. Quantities or variants outside the standard range are confirmed at quotation.
Storage & shipping
Parts are packed for export and shipped factory-direct to buyers in Europe, Asia, the Americas and the Middle East. Store fasteners dry and protected until installation, and keep coated parts in their packaging until use; specific packing and preservation requirements can be stated on the order and confirmed at quotation.
Frequently asked questions
This page and the legacy BS 3643 tolerance page overlap — which one governs?
They tabulate the same tolerance system from two editions, and the numbers agree wherever both print — the 6g external pitch-diameter band at M12 × 1.75 is 10.681/10.829 here and matches the modern limits inside the legacy ladder. The differences are coverage and presentation, not values: this page is the current-edition view (grade structure, deviation formulas, 6g/6H limits to M64) that modern drawings and gauges reference; the legacy page carries the machinery — class matrices by engagement length, the ISO 261 grid, worked examples for classes like 4h and 7H — and the full ladder to M300. For a drawing that names a modern class (6H/6g), this page and the BS 3643 limits ladder are your acceptance tables; for unusual classes or engagement conditions, use the legacy page's matrices. If a gauge and a drawing disagree, the drawing's stated edition governs — and that is exactly the information to put on the RFQ.
Related knowledge
- Thread-Forming vs Thread-Cutting vs Thread-Rolling Self-Tapping Screws: What the Evidence Settles on Base Material
- Screw Family Selection by Base Material: Wood, Machine and Self-Tapping Threads, Engagement and Coating
- Hex Bolts vs Socket Head Cap Screws: What the Evidence Settles on Strength, Clearance and Cost
Request a Quote
Get factory-direct pricing from the manufacturer.
What to include in your inquiry
- ✓ Standard and property class (e.g. DIN 912, ISO 4762, class 8.8) — or a drawing for custom parts.
- ✓ Sizes, lengths and thread type (metric or inch).
- ✓ Quantity per size and your target delivery date.
- ✓ Destination country, plus any coating or finish requirement.
- ✓ Any documents you need with the shipment (e.g. mill test certificate) so the quote includes them.
- ✓ Your inquiry goes straight to the factory team by email and gets a reply within 24 hours.
- ✓ Factory-direct pricing
- ✓ Standard and custom specifications
- ✓ Factory-direct export to buyers in Europe, Asia, the Americas and the Middle East
- ✓ Full fastener family support