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.
A ring has two size markings in millimeter such as 28mm-37mm, 49mm-52mm, 77mm-72mm and so on. The first number is the size of the thread that is closer to the camera lens (i.e. , the male thread), while the second is the size of the thread of the farther end (i.e. , the female thread). Therefore, a step-up ring with marking 43mm-49mm means the male and female thread sizes are 43mm and 49mm, respectively.