Metric Thread Dimensions and Tensile Stress Area Calculator
Whether you are programming a thread cycle or checking a bolt, you need the same few numbers: pitch diameter, minor diameter, thread depth and stress area. This calculator derives them from nominal diameter and pitch for any ISO metric thread, coarse or fine.
Your numbers
Coarse M10 is 1.5; fine M10 is 1.25 or 1.0.
Your results
Basic dimensions only. Tolerance classes (6g, 6H and others) change limits of size. Use ISO 898-1 and ISO 965 for acceptance data, and apply design safety factors.
Structure fastener data in your ERP
Optional: discuss cleaner item master data for fasteners and threaded parts.
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How to use it
Enter nominal diameter and pitch, then pick the property class of the fastener to see its minimum breaking load. The page returns the fundamental triangle height, basic pitch diameter, minor diameters for internal and external threads, thread depth and the tensile stress area. For turning, use the thread depth for the total infeed and divide it into passes; for design, use stress area and breaking load for the first strength check.
- Pitch is in mm: coarse M12 is 1.75, fine M12 is 1.25.
- d3 is the root diameter of the external thread, smaller than d1 of the nut.
- Breaking load is a minimum guarantee, not an allowable working load.
Formulas
From the ISO 68-1 profile, H = 0.866025 P. Basic pitch diameter d2 = d - 0.649519 P, basic minor diameter d1 = d - 1.082532 P. The external thread minor diameter d3 = d - 1.226869 P, and thread depth h3 = 0.613435 P. Tensile stress area per ISO 898-1 is As = pi / 4 x (d - 0.9382 P) squared, which sits between the pitch circle and minor circle areas.
Worked example
For M10 x 1.5: pitch diameter is 9.026 mm, d1 is 8.376 mm, d3 is 8.160 mm and thread depth is 0.920 mm. The stress area is 58.0 mm2, matching the standard figure. A class 8.8 bolt has a minimum breaking load around 46 kN, while class 10.9 reaches about 58 kN. A fine M10 x 1.25 has a larger stress area, about 61.2 mm2.
Common mistakes
Do not confuse the minor diameter of the bolt with the nut's minor diameter, and do not use basic sizes as the production target: tolerance class 6g leaves external threads slightly under basic. Another error is treating breaking load as working load; typical preload targets are 60 to 75 percent of proof load, which is itself below breaking load. For tapped holes in soft metals, thread engagement length matters as much as strength.
- Use limit dimensions from ISO 965 for inspection.
- Reduce infeed per pass as the thread deepens.
- Check stripping strength of the internal thread, not just the bolt.
Frequently Asked Questions
What is tensile stress area?
It is the effective cross-section used to compute thread strength. It sits between the minor and pitch circle areas to account for stress concentration at the root. ISO 898-1 defines it as As = pi/4 x (d - 0.9382P) squared.
Is M10 x 1.5 stress area 58 mm2?
Yes. The formula gives about 57.99 mm2, which rounds to the standard tabulated 58.0 mm2.
How deep should I cut a metric external thread?
The basic external thread depth is about 0.613 x pitch. For M10 x 1.5 that is 0.92 mm radially. Plan multiple passes with decreasing depth of cut, leaving a light finishing pass.
Does this cover inch UNC and UNF threads?
No. Inch threads use different constants and are specified in threads per inch. The profile is also 60 degrees, but stress area uses its own formula with TPI.
If fastener and thread data sit in item masters or drawings, Netray can help structure that data in your ERP so it can be searched and validated.
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