By Zencalcy Editorial TeamLast reviewed About us
Pitch diameter is the diameter where the thread thickness equals the space between threads — the dimension that actually controls fit. For an ISO metric thread it is d − 0.6495P; the external minor diameter is d − 1.2269P.
Metric thread pitch and minor diameters.
d₂ = d − 0.6495 P d₃ = d − 1.2269 P Aₛ = π/4 × (d − 0.9382P)²
These are basic dimensions before tolerance. External threads (bolts) run slightly smaller and internal threads slightly larger. The stress area As is what you use for tensile strength, not the nominal area.
| Symbol | Meaning |
|---|---|
| d | Nominal major diameter. |
| P | Thread pitch in millimetres. |
| d₂ | Pitch diameter. |
Pitch diameter 9.026 mm, minor diameter 8.160 mm and stress area 58.0 mm² — about 5,800 N capacity at 100 MPa.
Continue with the Beam Deflection Calculator, Beam Load Calculator, Bending Stress Calculator, or the Wood Beam Span Calculator — or browse more structural & workshop and all construction calculators.
Thread gauging and fit. A bolt and nut that match on pitch diameter will assemble and carry load evenly.
Results use standard construction estimating arithmetic: volumes from measured area and depth, unit weights from published material densities, and code-referenced spans or clearances where the page names a code. Quantities are rounded up to whole saleable units and include the stated waste allowance. These tools are planning aids, not structural design, and do not replace a licensed engineer, a local code check, or a contractor's site measurement.
Reference material used to build and check this calculator:
Last reviewed: September 2026. See how we build and check every tool on the about page.
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Content updated: September 2026