Mechanics · Machining

ISO metric thread basic dimensions

This page calculates only the ISO metric basic-profile geometry. It does not replace tolerance limits for classes such as 6H or 6g.

Created Sep 16, 2026v1.0

By Thibaut Grzelak, Mechanical Analysis Engineer

Machining

Results

Fundamental triangle height H

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Geometric height of the 60° fundamental triangle.

Pitch diameter d₂ / D₂

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Basic pitch diameter common to external and internal threads.

External minor diameter d₃

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Basic minor diameter of the external thread.

Internal minor diameter D₁

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Basic minor diameter of the internal thread.

Relation and numerical substitutionH = √3/2 · P ; d₂ = d − 3H/4

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ISO metric 60° profile. Nominal diameter and pitch use the same length unit. Results are basic dimensions: no fundamental deviation or tolerance-class allowance is applied. A standards-based tolerance check remains necessary for manufacturing or inspection.

01Formulas and symbols

Formulas used

H√3/2 · PFundamental triangle

d₂ = D₂d − 3H/4Basic pitch diameter

d₃d − 17H/12Basic external minor diameter

D₁d − 5H/4Basic internal minor diameter

02Assumptions and limits

Scope of validity

ISO metric 60° profile.
Nominal diameter and pitch use the same length unit.
Results are basic dimensions: no fundamental deviation or tolerance-class allowance is applied.
A standards-based tolerance check remains necessary for manufacturing or inspection.

03Validation example

Reference numerical case

For M10 × 1.5: H = 1.299038 mm.
d₂ = D₂ = 9.025721 mm; d₃ = 8.159697 mm; D₁ = 8.376202 mm.

04References

Technical references

ISO 68-1 — ISO general purpose metric screw threads — Basic profile.
ISO 724:2023 — ISO general purpose metric screw threads — Basic dimensions.
Tolerance classes are covered by standards including ISO 965 and are not calculated here.