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.
For Over 150 Years, The Standard of Accuracy. Calibrating external thread pitch diameter with three thread wires is a well-proven method and the most common one in use. Although any size wire between the minimum wire size and the maximum wire size may be used, common practice is to use the best wire size. This is the size that contacts the thread at the pitch diameter thus eliminating thread angle variation errors. 2. 3. For maximum accuracy, thread wire tolerances are very tight.