# The diameter of the thread is calculated metrically

When naming the diameter of a thread, basically two values come into question. The diameter that is measured at the thread tips and the value that indicates the distance between the indentations. The international standard for metric ISO threads defines the diameter at the thread crests as a nominal value.

For so-called metric coarse threads, the nominal value is given as a number marked with an M. With the exception of three nominal values with a small diameter, 1.2, 1.6 and 2.5 millimeters, all other sizes consist of natural numbers. The relationship to the thread diameter in the notch or thread determines the thread pitch.

Like the determination of the nominal value and the thread pitch, the flank angle of the metric standard thread is firmly defined. The angle of two adjacent thread flanks is sixty degrees. The nominal value minus the assigned pitch difference results in the theoretical diameter of the screwed object, nut or screw.