Dimension table
| Designation | Choice | Coarse pitch (mm) | Fine pitches (mm) | Drill, coarse pitch |
|---|---|---|---|---|
| M1 | 1 | 0.25 | 0.2 | 0.75 mm |
| M1.1 | 2 | 0.25 | 0.2 | 0.85 mm |
| M1.2 | 1 | 0.25 | 0.2 | 0.95 mm |
| M1.4 | 2 | 0.3 | 0.2 | 1.1 mm |
| M1.6 | 1 | 0.35 | 0.2 | 1.25 mm |
| M1.8 | 2 | 0.35 | 0.2 | 1.45 mm |
| M2 | 1 | 0.4 | 0.25 | 1.6 mm |
| M2.2 | 2 | 0.45 | 0.25 | 1.75 mm |
| M2.5 | 1 | 0.45 | 0.35 | 2.05 mm |
| M3 | 1 | 0.5 | 0.35 | 2.5 mm |
| M3.5 | 2 | 0.6 | 0.35 | 2.9 mm |
| M4 | 1 | 0.7 | 0.5 | 3.3 mm |
| M4.5 | 2 | 0.75 | 0.5 | 3.75 mm |
| M5 | 1 | 0.8 | 0.5 | 4.2 mm |
| M6 | 1 | 1 | 0.75 | 5 mm |
| M7 | 2 | 1 | 0.75 | 6 mm |
| M8 | 1 | 1.25 | 1, 0.75 | 6.75 mm |
| M10 | 1 | 1.5 | 1.25, 1, 0.75 | 8.5 mm |
| M12 | 1 | 1.75 | 1.5, 1.25, 1 | 10.25 mm |
| M14 | 2 | 2 | 1.5, 1.25*, 1 | 12 mm |
| M16 | 1 | 2 | 1.5, 1 | 14 mm |
| M18 | 2 | 2.5 | 2, 1.5, 1 | 15.5 mm |
| M20 | 1 | 2.5 | 2, 1.5, 1 | 17.5 mm |
| M22 | 2 | 2.5 | 2, 1.5, 1 | 19.5 mm |
| M24 | 1 | 3 | 2, 1.5, 1 | 21 mm |
| M27 | 2 | 3 | 2, 1.5, 1 | 24 mm |
| M30 | 1 | 3.5 | (3), 2, 1.5, 1 | 26.5 mm |
| M33 | 2 | 3.5 | (3), 2, 1.5 | 29.5 mm |
| M36 | 1 | 4 | 3, 2, 1.5 | 32 mm |
| M39 | 2 | 4 | 3, 2, 1.5 | 35 mm |
| M42 | 1 | 4.5 | (4), 3, 2, 1.5 | 37.5 mm |
| M45 | 2 | 4.5 | (4), 3, 2, 1.5 | 40.5 mm |
| M48 | 1 | 5 | (4), 3, 2, 1.5 | 43 mm |
| M52 | 2 | 5 | (4), 3, 2, 1.5 | 47 mm |
| M56 | 1 | 5.5 | 4, 3, 2, 1.5 | 50.5 mm |
| M60 | 2 | 5.5 | 4, 3, 2, 1.5 | 54.5 mm |
| M64 | 1 | 6 | 4, 3, 2, 1.5 | 58 mm |
Pitches per ISO 261, 1st and 2nd choice diameters; 3rd choice diameters such as M25 are not included. In parentheses: pitches best avoided. * M14×1.25 for spark plugs only. Drill = nominal diameter − pitch, not rounded to a catalog size; adjust for material and thread percentage.
Key technical characteristics
- Standard
- ISO 261 (general purpose)
- Range in this table
- M1 – M64, 1st and 2nd choice
- Designation
- M10 (coarse) · M10×1.25 (fine)
- Diameter choice
- Prefer 1st choice over 2nd
Typical applications
- Check which pitches a 1st or 2nd choice diameter has.
- Pick an available fine pitch for a given diameter.
- Review a drawing before quoting a threaded part.
Compatibility and interoperability
- ✗A fine-pitch thread will not fit a coarse-pitch thread of the same diameter: M10×1.25 and M10 are not interchangeable.
- ✓The same designation and tolerance class is interchangeable between manufacturers that meet the standard.
Selection guide
- 01If a drawing states no pitch, an M designation without a pitch means coarse pitch.
- 02If a diameter or pitch is not listed here, confirm with the shop that taps and gauges exist before you specify it.
Frequently Asked Questions
What does ISO 261 define?
It defines the nominal diameter and pitch combinations for general-purpose metric threads. Thread dimensions such as pitch and minor diameter come from the ISO 68-1 profile, and tolerances from ISO 965-1.
What is the pitch of an M10 thread?
The coarse pitch of M10 is 1.5 mm. Its fine pitches in ISO 261 are 1.25, 1, and 0.75 mm. A plain M10 designation means coarse pitch.
What do first and second choice mean?
They are diameter priorities within the standard. Use first-choice sizes such as M12 or M16 where you can, and second-choice sizes such as M14 or M18 only when the design calls for them.