Metric thread dimensions
The fetched Omni thread page derives ISO metric thread dimensions from the height of the fundamental triangle, H = P x sqrt(3) / 2.
Basic diameter formulas
d1 = d - 2 x (5/8) x H
d2 = d - 2 x (3/8) x H
Tolerance classes
Omni then applies tolerance grades and tolerance positions to determine the maximum and minimum major and pitch diameters. This rebuild follows the same external and internal ISO metric thread relationships for the core dimensions.