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.
If you see one sold as M3 x 1.5 x 10, it means the bolt is 3 mm in diameter, the thread count is 1.5 mm from crest to crest, and the length is 10 mm. Metric and standard nuts and bolts and can never be mixed. A screw is a type of bolt, but can also be self-tapping, like a woodscrew.