Metric Fine Thread Table
Common ISO metric fine pitches from M8 to M48 with tap drills, diameters and stress area.
A fine-pitch metric thread has the same nominal diameter as the coarse thread but a smaller pitch, and the pitch is written after the size: M12 x 1.5. Fine threads are used on thin-walled parts, on fasteners that must resist vibration, and where a fine adjustment is needed, such as on a micrometer, a fuel fitting or a wheel nut.
This table lists the fine pitches that are most often specified. For the coarse series see the metric thread table.
The table
| Thread | Major diameter (mm) | Fine pitch (mm) | Tap drill, about 75 percent thread (mm) | Pitch diameter (mm) | Minor diameter, external (mm) | Tensile stress area (mm2) |
|---|---|---|---|---|---|---|
| M8 x 1 | 8 | 1 | 7 | 7.35 | 6.773 | 39.17 |
| M10 x 1.25 | 10 | 1.25 | 8.75 | 9.188 | 8.466 | 61.2 |
| M10 x 1 | 10 | 1 | 9 | 9.35 | 8.773 | 64.49 |
| M12 x 1.5 | 12 | 1.5 | 10.5 | 11.026 | 10.16 | 88.13 |
| M12 x 1.25 | 12 | 1.25 | 10.75 | 11.188 | 10.466 | 92.07 |
| M14 x 1.5 | 14 | 1.5 | 12.5 | 13.026 | 12.16 | 124.55 |
| M16 x 1.5 | 16 | 1.5 | 14.5 | 15.026 | 14.16 | 167.25 |
| M18 x 1.5 | 18 | 1.5 | 16.5 | 17.026 | 16.16 | 216.23 |
| M20 x 1.5 | 20 | 1.5 | 18.5 | 19.026 | 18.16 | 271.5 |
| M22 x 1.5 | 22 | 1.5 | 20.5 | 21.026 | 20.16 | 333.06 |
| M24 x 2 | 24 | 2 | 22 | 22.701 | 21.546 | 384.42 |
| M27 x 2 | 27 | 2 | 25 | 25.701 | 24.546 | 495.74 |
| M30 x 2 | 30 | 2 | 28 | 28.701 | 27.546 | 621.2 |
| M36 x 3 | 36 | 3 | 33 | 34.051 | 32.319 | 864.94 |
| M42 x 3 | 42 | 3 | 39 | 40.051 | 38.319 | 1205.98 |
| M48 x 3 | 48 | 3 | 45 | 46.051 | 44.319 | 1603.56 |
Source and notes: ISO 261 and ISO 724 (selected fine pitches), same formulas as the coarse table.
How to use this table
- Find the thread in the first column, for example M12 x 1.5.
- Drill a tapped hole with the tap drill size shown (about 75 percent thread).
- Use the tensile stress area to find the proof load or breaking load of a bolt.
Worked example: M12 fine against M12 coarse
- Coarse M12: pitch 1.75 mm, tensile stress area 84.3 mm².
- Fine M12 x 1.5: tensile stress area 88.1 mm², tap drill 10.5 mm.
- The fine thread has 4.6 percent more stress area, so a class 8.8 bolt carries about 2.2 kN more proof load.
Notes and cautions
- Fine-pitch fasteners are less common, so check availability before specifying them.
- Tightening torque for a given preload depends on the pitch as well as the diameter, so enter the fine pitch in the bolt torque tool rather than using a coarse-thread rule of thumb.
Related tools and guides
- Tap Drill Size and Thread Pitch Lookup
- Bolt Torque and Thread Engagement Tool
- Bolted and Welded Joints (guide)
- All reference tables
FAQ
When should I use a fine thread?
When you need more strength from a small diameter, resistance to vibration loosening, fine adjustment, or a thread cut into a thin wall. Otherwise the coarse thread is cheaper, more available and more forgiving.
How do I find the tap drill for a fine thread?
Subtract the pitch from the diameter: for M12 x 1.5 that is 12 − 1.5 = 10.5 mm. The table lists it for every pitch shown.
Sources
- ISO 261 and ISO 724 (metric threads, selected fine pitches).
- ISO 261 and ISO 724 (selected fine pitches), same formulas as the coarse table.