Personally, I think AICC should be punted over the goal post of so long compliance standards. and some vendors like to offer multiple choices, and yes AICC does different things, but so does driving a moped and I rarely seen people cruising down the interstate on one (unless you live in LA).
Part One: How to Measure Thread Size. 1  In general, the thread should match the fabric in size and weight. For heavier, thicker fabrics, use heavier thread. 2  Heavier threads create more visible stitches. 3  V-69 is the heaviest size recommended for sewing machines. 4  Heavier threads are stronger.
(CHART IV): TAP DRILL FORMULA FOR METRIC THREADS; NOMINAL OD OF THREAD (MAJOR DIAMETER) - PITCH = TAP DRILL SIZE. (Note: This formula will yield approximately 68% - 77% of thread.) Example: TO FIND THE TAP DRILL SIZE FOR AN M10 x 1.5 THREAD. 10 (OD) - 1.5 (PITCH) = 8.5 mm (TAP DRILL SIZE).