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.
Threads - Metric ISO 724. M Thread (metric ISO 724 thread) European Standard. The European Standard M Thread - ISO 724:1993 ISO general-purpose metric screw threads -- Basic dimensions (DIN 13) is recognizable by its cylindrical outer and inner diameter in millimeters. The thread angle is 60o. The thread depth is 0.614 x pitch.