Metric thread dimensions
Pitch, major and minor diameters, and tensile stress area for metric coarse threads. The tensile stress area is the value to use when working out how much load a metric bolt or stud can carry.
Metric coarse thread dimensions
| Size | Pitch (mm) | Major dia (mm) | Minor dia (mm) | Stress area (mm²) |
|---|---|---|---|---|
| M3 | 0.5 | 3.0 | 2.387 | 5.03 |
| M4 | 0.7 | 4.0 | 3.141 | 8.78 |
| M5 | 0.8 | 5.0 | 4.019 | 14.2 |
| M6 | 1.0 | 6.0 | 4.773 | 20.1 |
| M8 | 1.25 | 8.0 | 6.466 | 36.6 |
| M10 | 1.5 | 10.0 | 8.160 | 58.0 |
| M12 | 1.75 | 12.0 | 9.853 | 84.3 |
| M14 | 2.0 | 14.0 | 11.546 | 115 |
| M16 | 2.0 | 16.0 | 13.546 | 157 |
| M20 | 2.5 | 20.0 | 16.933 | 245 |
| M24 | 3.0 | 24.0 | 20.319 | 353 |
Major diameter equals the nominal size (M8 is 8 mm across the crests). Minor diameter is across the roots, close to the tap drill size. Multiply the tensile stress area by the bolt proof or yield strength in MPa to get the load capacity in newtons. These are coarse-pitch threads; fine pitches have slightly larger stress areas.
Need the tap drill or inch threads?
See the Tap Drill Calculator for hole sizes, or the Unified Thread Dimensions for inch sizes.
Using stress area for metric bolts
To find the strength of a metric bolt, multiply its tensile stress area in square millimeters by the strength in MPa, which gives the force in newtons. An M8 bolt of class 8.8 has a stress area of 36.6 and a proof strength near 600, so it carries roughly 22,000 newtons before yielding. This is why stress area, not the 8 mm nominal size, drives the calculation.
Coarse and fine threads
These values are for coarse threads, the default for most metric bolts. Fine-pitch threads of the same nominal size have a slightly larger minor diameter and stress area, so they are marginally stronger in tension and resist loosening better, at the cost of being easier to cross-thread.
FAQ
What is the stress area of an M10 bolt?
About 58 square millimeters for the coarse M10 x 1.5 thread. Multiply by the strength in MPa to get capacity in newtons.
What is the minor diameter of M8?
About 6.47 mm for the coarse M8 x 1.25 thread, which sets the tap drill size near 6.8 mm.
How do I find a metric bolt strength?
Multiply the tensile stress area in square millimeters by the property-class strength in MPa. The result is the load in newtons.