ISO Metric Fine Thread Specifications
Industry Standard: ISO 261 / ISO 965
ISO metric fine threads have a smaller pitch (more threads per unit length) compared to coarse threads. Fine threads are commonly used in applications requiring higher tensile strength, finer adjustments, or thin-walled assemblies where coarse threads would strip or penetrate too deeply.
| Size | Ø Major (mm) | Pitch (mm) | Ø Pitch (mm) | Ø Minor (Ext) | Tap Drill (75%) | Stress Area (mm²) |
|---|---|---|---|---|---|---|
| M1.6x0.35 | 1.60 | 0.35 | 1.373 | 1.221 | 1.25 | 1.27 |
| M2x0.25 | 2.00 | 0.25 | 1.838 | 1.729 | 1.75 | 2.45 |
| M2.5x0.35 | 2.50 | 0.35 | 2.273 | 2.121 | 2.15 | 3.70 |
| M3x0.35 | 3.00 | 0.35 | 2.773 | 2.621 | 2.65 | 5.61 |
| M4x0.5 | 4.00 | 0.50 | 3.675 | 3.459 | 3.50 | 9.79 |
| M5x0.5 | 5.00 | 0.50 | 4.675 | 4.459 | 4.50 | 16.12 |
| M6x0.75 | 6.00 | 0.75 | 5.513 | 5.188 | 5.25 | 22.03 |
| M8x1 | 8.00 | 1.00 | 7.350 | 6.917 | 7.00 | 39.17 |
| M10x1.25 | 10.00 | 1.25 | 9.188 | 8.647 | 8.75 | 61.20 |
| M10x1 | 10.00 | 1.00 | 9.350 | 8.917 | 9.00 | 64.49 |
| M12x1.5 | 12.00 | 1.50 | 11.026 | 10.376 | 10.50 | 88.13 |
| M12x1.25 | 12.00 | 1.25 | 11.188 | 10.647 | 10.75 | 92.07 |
| M14x1.5 | 14.00 | 1.50 | 13.026 | 12.376 | 12.50 | 124.55 |
| M16x1.5 | 16.00 | 1.50 | 15.026 | 14.376 | 14.50 | 167.25 |
| M18x2 | 18.00 | 2.00 | 16.701 | 15.835 | 16.00 | 204.18 |
| M18x1.5 | 18.00 | 1.50 | 17.026 | 16.376 | 16.50 | 216.23 |
| M20x2 | 20.00 | 2.00 | 18.701 | 17.835 | 18.00 | 257.98 |
| M20x1.5 | 20.00 | 1.50 | 19.026 | 18.376 | 18.50 | 271.50 |
| M22x2 | 22.00 | 2.00 | 20.701 | 19.835 | 20.00 | 318.05 |
| M22x1.5 | 22.00 | 1.50 | 21.026 | 20.376 | 20.50 | 333.06 |
| M24x2 | 24.00 | 2.00 | 22.701 | 21.835 | 22.00 | 384.42 |
| M27x2 | 27.00 | 2.00 | 25.701 | 24.835 | 25.00 | 495.74 |
| M30x2 | 30.00 | 2.00 | 28.701 | 27.835 | 28.00 | 621.20 |
| M33x2 | 33.00 | 2.00 | 31.701 | 30.835 | 31.00 | 760.80 |
| M36x3 | 36.00 | 3.00 | 34.051 | 32.752 | 33.00 | 864.94 |
| M39x3 | 39.00 | 3.00 | 37.051 | 35.752 | 36.00 | 1028.39 |
| M42x3 | 42.00 | 3.00 | 40.051 | 38.752 | 39.00 | 1205.98 |
| M45x3 | 45.00 | 3.00 | 43.051 | 41.752 | 42.00 | 1397.70 |
| M48x3 | 48.00 | 3.00 | 46.051 | 44.752 | 45.00 | 1603.56 |
| M52x3 | 52.00 | 3.00 | 50.051 | 48.752 | 49.00 | 1900.04 |
| M56x4 | 56.00 | 4.00 | 53.402 | 51.670 | 52.00 | 2143.96 |
| M60x4 | 60.00 | 4.00 | 57.402 | 55.670 | 56.00 | 2484.80 |
| M64x4 | 64.00 | 4.00 | 61.402 | 59.670 | 60.00 | 2850.78 |
| M68x4 | 68.00 | 4.00 | 65.402 | 63.670 | 64.00 | 3241.89 |
Standard FAQs
Why use metric fine threads instead of coarse?
Fine threads have a larger minor diameter, which gives the bolt a larger cross-sectional stress area and higher shear strength. They are also less likely to loosen under vibration and allow for precise adjustments.
Are metric coarse and fine threads compatible?
No. Coarse and fine threads of the same nominal diameter (e.g., M10x1.5 Coarse vs. M10x1.25 Fine) have different pitches and will cross-thread and damage each other if forced together.