Thread & Fastener Size Reference
Pick an ISO metric size to see its major diameter, coarse and fine pitch, tap-drill size, and tensile stress area — or compute the stress area for any diameter and pitch of your own.
M10 thread data
Custom tensile stress area
ISO metric coarse-thread table
| Size | Major dia (mm) | Coarse pitch (mm) | Fine pitch (mm) | Tap drill (mm) | Stress area (mm²) |
|---|---|---|---|---|---|
| M3 | 3 | 0.5 | 0.35 | 2.5 | 5.03 |
| M4 | 4 | 0.7 | 0.5 | 3.3 | 8.78 |
| M5 | 5 | 0.8 | 0.5 | 4.2 | 14.18 |
| M6 | 6 | 1 | 0.75 | 5 | 20.12 |
| M8 | 8 | 1.25 | 1 | 6.8 | 36.61 |
| M10 | 10 | 1.5 | 1.25 | 8.5 | 57.99 |
| M12 | 12 | 1.75 | 1.25 | 10.2 | 84.27 |
| M14 | 14 | 2 | 1.5 | 12 | 115.44 |
| M16 | 16 | 2 | 1.5 | 14 | 156.67 |
| M20 | 20 | 2.5 | 1.5 | 17.5 | 244.79 |
| M24 | 24 | 3 | 2 | 21 | 352.5 |
How to use this reference
Selecting a size shows the numbers you reach for when specifying or identifying a fastener: the nominal major diameter, the standard coarse pitch and a common fine pitch, the recommended tap-drill diameter for the coarse thread, and the tensile stress area. The stress area is derived from the ISO 898 formula rather than tabulated, so it always matches the value the bolt-torque calculator uses.
The custom section applies the same formula to any diameter and pitch you type in, and the full table lets you scan M3 through M24 at a glance. Every figure is a reference value; confirm tap-drill choices against the thread-fit class and the material being cut.
Frequently Asked Questions
What is the difference between coarse and fine pitch?
Pitch is the distance from one thread crest to the next. A coarse thread has a larger pitch and fewer threads per length; a fine thread packs more threads into the same length. Coarse threads are quicker to run and more tolerant of damage and coatings, so they are the default for general assembly. Fine threads give slightly more clamp force and resist loosening under vibration, which is why they appear on precision and aerospace fasteners.
What is a tap drill and how do I use this table?
A tap drill is the hole you drill before cutting an internal thread with a tap. It must be a little larger than the thread's root so the tap forms a strong but complete thread. The tap-drill column here gives the standard size for each coarse thread — for example a 6.8 mm drill for an M8 coarse thread. Confirm against the thread-fit class and the material you are cutting.
What is the tensile stress area?
The tensile stress area is the effective cross-section of a threaded fastener that actually carries axial load. It is smaller than the plain shank because the thread reduces the load-bearing metal, and larger than the root area because of the way the threads share load. It is the figure used to turn a material's strength into a bolt's proof and clamp loads, so it links directly to the bolt-torque calculation.
How is the stress area computed for a custom thread?
The custom section uses the ISO 898 formula: take the nominal diameter, subtract 0.9382 times the pitch to get the effective stress diameter, then take the area of a circle of that diameter. Enter any diameter and pitch in millimetres and the tool returns the stress area in square millimetres — useful for non-standard or imperial threads converted to metric units.
Educational reference only. Values are standard nominal figures rounded for display; verify any thread or tap-drill choice that matters for assembly or safety against the applicable standard and material.