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.
The UN specification specifies that the common height of a thread should be 5/8th of this maximum height. 75% to 80% thread roughly equals 5/8th of this maximum height. NOTE: If tapping idfficult to machine materials or using small taps, use a lower thread percentage such as 60% to 70%.