How this calculator works
For a 60 degree basic metric profile, the pitch diameter lies 3H/4 below the major diameter, where H is the fundamental triangle height. External upper deviation sets the largest external size; internal lower deviation sets the smallest internal size. Zero tolerance defaults show basic geometry only.
Formula
H = sqrt(3)P/2; d2 = D2 = d - 3H/4 = d - 0.6495190528P; external limits = d2+es and d2+es-T; internal limits = D2+EI and D2+EI+T.
Worked example
M10 x 1.5 has basic pitch diameter 10 - 0.6495190528 x 1.5 = 9.02572142 mm. A supplied -0.032 mm upper deviation and 0.132 mm width give external limits 8.86172142 to 8.99372142 mm.
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Frequently asked questions
Does this select a 6g or 6H tolerance?
No. Obtain the required deviations and tolerance widths from the applicable ISO 965 table or controlled drawing.
Why do both thread sides share a basic diameter?
The theoretical profile is common. Actual mating clearance comes from the deviations and tolerance widths.
Does this apply to pipe threads?
No. This page uses a straight 60 degree ISO metric basic profile.