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.
#12. Diameters 1/4 inch and larger are converted from decimals to fractions in 1/16 inch increments. a) MAJOR DIAMETER: The largest diameter of a screw thread; measured from the crests on external threads and the roots on internal threads.b) PITCH DIAMETER: The imaginary diameter equal distance between the major and minor diameters.) MINOR DIAMETER: The smaller diameter of a screw thread; measured from the roots on external threads and the crests on internal threads. d) THREAD PITCH: The distance between a given point on a thread and a corresponding point on the next thread.