Standard Thread Sizes (UNC/UNF & Metric) Table
Design parameters for metric coarse and unified national standard threads including pitch, major, pitch, and minor diameters.
Overview & Scope
Thread profiles detail pitch, external root / minor diameters, and tensile stress areas for standard metric and unified national thread series per ISO 68-1 and ASME B1.1 / Machinery's Handbook (31st Edition). The tensile stress area dictates the fastener's load capacity under axial tension and preload.
Technical Sizing Values
The table below specifies major, pitch, and explicit external root / minor diameters alongside nominal tensile stress areas calculated per ASME B1.1 and ISO 898-1 standards.
| Thread Designation | Major Diameter (mm) | Major Diameter (in) | Pitch Diameter (mm) | Pitch Diameter (in) | Calculated External Root Reference Diameter (mm) | Calculated External Root Reference Diameter (in) | Tensile Stress Area (mm²) | Tensile Stress Area (in²) |
|---|---|---|---|---|---|---|---|---|
| M6 x 1.0 (Coarse) | 6 | 0.236 | 5.35 | 0.211 | 4.77 | 0.188 | 20.1 | 0.031 |
| M8 x 1.25 (Coarse) | 8 | 0.315 | 7.19 | 0.283 | 6.47 | 0.255 | 36.6 | 0.057 |
| M10 x 1.5 (Coarse) | 10 | 0.394 | 9.03 | 0.355 | 8.16 | 0.321 | 58 | 0.09 |
| M12 x 1.75 (Coarse) | 12 | 0.472 | 10.86 | 0.428 | 9.85 | 0.388 | 84.3 | 0.131 |
| 1/4-20 UNC | 6.35 | 0.25 | 5.54 | 0.2181 | 4.97 | 0.1957 | 20.5 | 0.0318 |
| 3/8-16 UNC | 9.53 | 0.375 | 8.49 | 0.3343 | 7.8 | 0.3071 | 50 | 0.0775 |
| 1/2-13 UNC | 12.7 | 0.5 | 11.43 | 0.45 | 10.59 | 0.4169 | 91.5 | 0.1419 |
| 5/8-11 UNC | 15.88 | 0.625 | 14.38 | 0.566 | 13.38 | 0.5268 | 146 | 0.226 |
| 3/4-10 UNC | 19.05 | 0.75 | 17.4 | 0.685 | 16.3 | 0.6417 | 216 | 0.334 |
| 7/8-9 UNC | 22.23 | 0.875 | 20.39 | 0.8028 | 19.18 | 0.7547 | 298 | 0.462 |
| 1-8 UNC | 25.4 | 1 | 23.34 | 0.9188 | 21.97 | 0.8647 | 391 | 0.606 |
| 1 1/4-7 UNC | 31.75 | 1.25 | 29.39 | 1.1572 | 27.84 | 1.0957 | 625 | 0.969 |
| 1 1/2-6 UNC | 38.1 | 1.5 | 35.36 | 1.3917 | 33.58 | 1.3218 | 906 | 1.405 |
Engineering Notes & Best Practices
- •Tensile stress area (A_s) is calculated per ASME B1.1 (A_s = (π/4)·(d - 0.9743/n)²) and ISO 898-1, accounting for the helical thread pitch profile.
- •External minor diameter (d₃) represents the external thread root diameter with flat root profile (d₃ = d - 1.226869/n for UN series per Machinery's Handbook 31st Edition).
- •Metric coarse and UNC threads offer higher resistance to stripping in soft materials.
- •UNF fine threads provide finer adjustments and higher vibration loosening resistance.
Dataset Citations & References
ASME B1.1 Unified Inch Screw Threads
Public domain source and standard catalog reference parameters.
Machinery's Handbook (31st Edition)
Public domain source and standard catalog reference parameters.
ISO 68-1 Thread Profiles
Public domain source and standard catalog reference parameters.