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.
Determine the thread pitch by counting the threads along the shaft. Do this by measuring one inch of the shaft and counting how many threads (a rise and depth is one thread) are in that inch. In the example, there are 12 threads per inch, so the measure reads as 12. Measure the length of the shank. The length of the shank is from the point where it meets the head to the opposite end.