Metric Thread Tensile Stress Area Chart
Tensile stress area for metric coarse and fine threads — the figure you multiply by the bolt strength class to get its load capacity.
| Nominal dia. (mm) | Coarse pitch (mm) | Coarse stress area (mm²) | Fine pitch (mm) | Fine stress area (mm²) |
|---|
Standard: ISO 898-1 / ISO 724 · Data checked: 2026-10-14
Frequently asked questions
Why is stress area smaller than the shank area?
Because a bolt almost always fails through the threaded portion, where the cross-section is reduced by the thread itself. Stress area is the effective area through the threads, calculated from the mean of pitch and minor diameter — so it is smaller than the shank and it is the number to use for load.
How do I get the load capacity of a bolt from this?
Multiply the stress area by the bolt's minimum tensile strength. An M12 class 8.8 bolt has a coarse stress area of 84.3 mm2 and a minimum tensile of 800 MPa, so about 67 kN. Use the yield strength and a safety factor instead if you are sizing for a working load.
Why is the fine thread stress area larger?
A finer pitch removes less material, so the minor diameter is bigger and the stress area with it. That is why fine threads are preferred where fatigue or vibration matters — M12 x 1.25 has 92.1 mm2 against 84.3 mm2 for M12 x 1.75.
Can I just use the shank diameter instead?
No, it overstates capacity by roughly 30% because the thread reduces the cross-section. A calculation based on nominal diameter will tell you a joint is safe when it is not — this is exactly the kind of error that shows up as a sheared bolt.