ISO 724 Metric Thread Basic Dimensions (M1.6 - M100)
ISO 724 basic thread dimensions for the general-purpose coarse series, M1.6 - M100: pitch, basic major diameter d = D, basic pitch diameter d2 = D2 and basic internal minor diameter D1 per size — the theoretical thread geometry behind stress-area and tapping calculations.
Last updated: 2026-11
Specifications
Basic dims are the thread before tolerances: the theoretical values a perfect thread holds, and the numbers most design calculations want. This collected page tabulates ISO 724 for the general-purpose coarse series across 34 sizes, M1.6 (0.35 pitch) through M100 (6 pitch): basic pitch P, basic major d = D (the nominal, printed without trailing zeros on integer sizes as the source does), basic pitch diameter d2 = D2 (M6: 5.350; M12: 10.863; M30: 27.727; M64: 60.103), and basic internal minor D1 (M6: 4.917; M12: 10.106; M64: 57.505). The D1 column is the tapping-theory anchor — drill sizes derive from it — and the d2 column feeds every stress-area and thread-stripping calculation (the tensile-stress-area ladder on our metric-thread-stress page builds on these values). Three companions in this family complete the picture: the ISO 965 page adds the tolerance system, the legacy BS 3643 ladder adds the 6g/6H manufacturable bands, and the ISO 262 page (pitch selection) already covers which pitch pairs with which size. The page's own standards index is carried as the first table. Materials and strength are not tabulated — per RFQ.
| Size range | M1.6 - M100 coarse series, 34 sizes: pitch 0.35 (M1.6) to 6 (M64 - M100) |
|---|---|
| Basic pitch diameter d2 = D2 | M1.6: 1.373; M6: 5.350; M12: 10.863; M30: 27.727; M100: 96.103 |
| Basic internal minor D1 | M1.6: 1.221; M6: 4.917; M12: 10.106; M30: 26.211; M100: 93.505 |
| Notation | mm; integer major diameters print without trailing zeros (e.g. "2", "3") — carried verbatim |
| Companions | ISO 965 tolerance classes, legacy BS 3643 6g/6H limits ladder, ISO 262 pitch selection — all in this family |
| Not tabulated | Tolerance bands, limits of size, fine-pitch series, thread strength — per RFQ |
| Standard | Engineering purpose |
|---|---|
| ISO 68-1:2023 | Basic and design profiles for metric screw threads. |
| ISO 261:1998 | General plan of diameter/pitch combinations. |
| ISO 262:2023 | Selected commercial fastener sizes from M1 to M100. |
| ISO 724:2023 | Basic dimensions. |
| ISO 965-1:2026 | Tolerance system, positions, grades, recommended classes and designation. |
| ISO 965-2:2024 | Limits of sizes for 6H/6g from M1.6 to M100 and 5H/6h from M1 to M1.4. |
| Thread | Pitch P mm | Basic major diameter d = D mm | Basic pitch diameter d 2 = D 2 mm | Basic internal minor diameter D 1 mm |
|---|---|---|---|---|
| M1.6 | 0.35 | 1.6 | 1.373 | 1.221 |
| M1.8 | 0.35 | 1.8 | 1.573 | 1.421 |
| M2 | 0.4 | 2 | 1.740 | 1.567 |
| M2.2 | 0.45 | 2.2 | 1.908 | 1.713 |
| M2.5 | 0.45 | 2.5 | 2.208 | 2.013 |
| M3 | 0.5 | 3 | 2.675 | 2.459 |
| M3.5 | 0.6 | 3.5 | 3.110 | 2.850 |
| M4 | 0.7 | 4 | 3.545 | 3.242 |
| M4.5 | 0.75 | 4.5 | 4.013 | 3.688 |
| M5 | 0.8 | 5 | 4.480 | 4.134 |
| M6 | 1 | 6 | 5.350 | 4.917 |
| M7 | 1 | 7 | 6.350 | 5.917 |
| M8 | 1.25 | 8 | 7.188 | 6.647 |
| M10 | 1.5 | 10 | 9.026 | 8.376 |
| M12 | 1.75 | 12 | 10.863 | 10.106 |
| M14 | 2 | 14 | 12.701 | 11.835 |
| M16 | 2 | 16 | 14.701 | 13.835 |
| M18 | 2.5 | 18 | 16.376 | 15.294 |
| M20 | 2.5 | 20 | 18.376 | 17.294 |
| M22 | 2.5 | 22 | 20.376 | 19.294 |
| M24 | 3 | 24 | 22.051 | 20.752 |
| M27 | 3 | 27 | 25.051 | 23.752 |
| M30 | 3.5 | 30 | 27.727 | 26.211 |
| M33 | 3.5 | 33 | 30.727 | 29.211 |
| M36 | 4 | 36 | 33.402 | 31.670 |
| M39 | 4 | 39 | 36.402 | 34.670 |
| M42 | 4.5 | 42 | 39.077 | 37.129 |
| M48 | 5 | 48 | 44.752 | 42.587 |
| M56 | 5.5 | 56 | 52.428 | 50.046 |
| M64 | 6 | 64 | 60.103 | 57.505 |
| M72 | 6 | 72 | 68.103 | 65.505 |
| M80 | 6 | 80 | 76.103 | 73.505 |
| M90 | 6 | 90 | 86.103 | 83.505 |
| M100 | 6 | 100 | 96.103 | 93.505 |
Materials
- Basic dims are material-independent. What pairs with them in practice: tapping a D1-derived drill into the softer of the two mating materials, and specifying thread class so the manufactured bands (not these theoretical values) govern acceptance. RFQ threaded parts with size, pitch and class; calculation-grade thread data requests are welcome through the inquiry line
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 724 Metric Thread Basic Dimensions (M1.6 - M100)) 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
These are called "basic" dimensions — how do they relate to the actual measured size of a bolt or nut?
A real fastener never sits exactly on the basic values — it lives inside tolerance bands that hang off them. For the external thread, the whole band sits below basic (the 6g fundamental deviation pulls it down so the bolt clears the nut); for the internal thread the band starts at basic and goes up (6H). On the pitch diameter at M10 x 1.5: basic is 9.026 on this page, while the manufactured 6g bolt band is 8.862 - 8.994 and the 6H nut band is 9.026 - 9.198 — both traceable on the companion tolerance pages. That is why you measure a brand-new M10 bolt at ~9.97 mm across the threads, not 10.000: the major-diameter band (9.732 - 9.968) is deliberately below nominal. Use this page for the design-side numbers (stress areas, drill selection, clearance-hole sizing), and the tolerance pages for manufacture and gauging — mixing a basic value into a fit calculation is the usual way double-clearance errors creep in.
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