Thread pitch chart - M1.6 to M64 (ISO 261)
Verified by Rachel Mayfield, Supply Chain Analyst - April 2026
Metric thread pitch and tap drill sizes for M1.6 through M64, covering both coarse and fine pitch series per ISO 261 and ISO 724. Metric Thread Pitch Chart Tap drill sizes are calculated as nominal diameter minus pitch (e.g. M10 x 1.5 coarse = 10 - 1.5 = 8.5 mm drill). Where multiple fine pitches exist, the most common options are listed.
| Size | Coarse Pitch (mm) | Fine Pitch (mm) | Tap Drill Coarse (mm) | Tap Drill Fine (mm) |
|---|---|---|---|---|
| M1.6 | 0.35 | 0.2 | 1.25 | 1.4 |
| M2 | 0.4 | 0.25 | 1.6 | 1.75 |
| M2.5 | 0.45 | 0.35 | 2.05 | 2.15 |
| M3 | 0.5 | 0.35 | 2.5 | 2.65 |
| M4 | 0.7 | 0.5 | 3.3 | 3.5 |
| M5 | 0.8 | 0.5 | 4.2 | 4.5 |
| M6 | 1.0 | 0.75 | 5.0 | 5.25 |
| M8 | 1.25 | 1.0 / 0.75 | 6.8 | 7.0 / 7.25 |
| M10 | 1.5 | 1.25 / 1.0 | 8.5 | 8.75 / 9.0 |
| M12 | 1.75 | 1.5 / 1.25 | 10.2 | 10.5 / 10.75 |
| M14 | 2.0 | 1.5 | 12.0 | 12.5 |
| M16 | 2.0 | 1.5 | 14.0 | 14.5 |
| M18 | 2.5 | 2.0 / 1.5 | 15.5 | 16.0 / 16.5 |
| M20 | 2.5 | 2.0 / 1.5 | 17.5 | 18.0 / 18.5 |
| M22 | 2.5 | 2.0 / 1.5 | 19.5 | 20.0 / 20.5 |
| M24 | 3.0 | 2.0 | 21.0 | 22.0 |
| M27 | 3.0 | 2.0 | 24.0 | 25.0 |
| M30 | 3.5 | 2.0 | 26.5 | 28.0 |
| M33 | 3.5 | 2.0 | 29.5 | 31.0 |
| M36 | 4.0 | 3.0 | 32.0 | 33.0 |
| M39 | 4.0 | 3.0 | 35.0 | 36.0 |
| M42 | 4.5 | 3.0 | 37.5 | 39.0 |
| M45 | 4.5 | 3.0 | 40.5 | 42.0 |
| M48 | 5.0 | 3.0 | 43.0 | 45.0 |
| M52 | 5.0 | 4.0 | 47.0 | 48.0 |
| M56 | 5.5 | 4.0 | 50.5 | 52.0 |
| M60 | 5.5 | 4.0 | 54.5 | 56.0 |
| M64 | 6.0 | 4.0 | 58.0 | 60.0 |
How to use the metric thread pitch chart
To identify an unknown metric thread, measure the major (outside) diameter with calipers, then check the pitch with a thread pitch gauge. Match both values against this table to confirm the thread size. Coarse pitch is the default - if a drawing says M10 with no pitch specified, it means M10 x 1.5 coarse.
Fine pitch threads are used where vibration resistance matters (automotive, aerospace) or where thin wall sections need a shallower thread. They need a larger tap drill because the thread depth is smaller.
Tap drill sizes shown give approximately 75% thread engagement, which is the standard for most engineering applications. Going smaller (higher engagement) increases tapping torque and tap breakage risk without adding meaningful strength.
Related standards
- ISO 261 - ISO general-purpose metric screw threads: general plan
- ISO 724 - ISO metric screw threads: basic dimensions
- BS 3643 - ISO metric screw threads (UK implementation)
- ISO 2306 - Machine and hand taps for ISO metric threads
- BS 949 - Specification for parallel shanked twist drills for tapping size holes
References
- ISO 261:1998 - ISO metric screw threads - general plan
- ISO 724:1993 - ISO metric screw threads - basic dimensions
- British Standards Institution
Frequently Asked Questions
What is the tap drill size for M10 coarse?
The tap drill for M10 x 1.5 coarse pitch is 8.5 mm. This gives approximately 75% thread engagement, which is the standard recommendation for most materials.
What is the difference between coarse and fine metric threads?
Coarse pitch is the default thread series with larger pitch (e.g. M10 x 1.5). Fine pitch has a smaller pitch (e.g. M10 x 1.25 or 1.0), giving better vibration resistance, higher tensile strength for the same bolt size, and suitability for thin-walled components. Coarse is easier to assemble and more tolerant of damaged threads.
How do I calculate the tap drill size for a metric thread?
For 75% thread engagement, subtract the pitch from the nominal diameter. For M12 x 1.75 coarse: 12 - 1.75 = 10.25 mm, rounded to 10.2 mm standard drill. For M12 x 1.25 fine: 12 - 1.25 = 10.75 mm drill.
What is the standard coarse pitch for a M10 screw according to the Thread pitch chart - M1.6 to M64 (ISO 261)?
The standard coarse pitch for a M10 screw, as per the Thread pitch chart - M1.6 to M64 (ISO 261), is 1.5 mm.
What are the fine pitch options available for a M8 screw in the Thread pitch chart - M1.6 to M64 (ISO 261)?
The Thread pitch chart - M1.6 to M64 (ISO 261) lists two fine pitches for a M8 screw, which are 1.0 mm and 0.75 mm.
How is the tap drill size calculated for the coarse series of threads in the Thread pitch chart - M1.6 to M64 (ISO 261)?
The tap drill size for the coarse series of threads is determined by subtracting the pitch from the nominal diameter, as detailed in the Thread pitch chart - M1.6 to M64 (ISO 261).
What are some UK suppliers that provide screws adhering to the ISO 724 standard covered in the Thread pitch chart - M1.6 to M64 (ISO 261)?
Popular UK suppliers like Screwfix and RS Components offer a variety of metric screws that comply with ISO 724 standards listed in the Thread pitch chart - M1.6 to M64 (ISO 261).
What is the fine pitch for a M3 screw as per the Thread pitch chart - M1.6 to M64 (ISO 261)?
The fine pitch for a M3 screw, according to the Thread pitch chart - M1.6 to M64 (ISO 261), is 0.35 mm.
How do you choose between coarse and fine pitches when using the Thread pitch chart - M1.6 to M64 (ISO 261)?
When selecting between coarse and fine pitches, consider the application's strength requirements; fine threads offer better resistance to loosening but require more turns for assembly.
What is the cost or availability of metric screws listed in the Thread pitch chart - M1.6 to M64 (ISO 261)?
The cost and availability of metric screws vary based on size, material, and quantity; larger sizes like M30 and above may require longer lead times and higher costs due to less common usage compared to smaller sizes listed in the Thread pitch chart - M1.6 to M64 (ISO 261).