Ply count refers to the total amount of layered cloth pieces used in the buffing wheel construction. Typically, 40 ply buffing wheels would be a bit under a 1/2" in thickness.
Stitching is measured either in total concentric rows of sewing or the inches in space between each row of sewing. Keep in mind, the tighter the the sewing, the more aggressive and tight the buffing wheel will polish. Also, it can be advantageous to get a tighter sewing pattern since rows of sewing can be removed with a small knife allowing the user to always "loosen" the sewn buffing wheel and get a softer polish if needed.
These cotton sewn polishing wheels need to have compound applied while the buffing wheel is spinning. Given their thicker and stout stack of cotton material sewn together, it's important to use a buffing wheel rake often if the compound somewhat solidifies during use on the end of the polishing wheel. A hard tacky surface of compound that has built up can be indicative of a need to use a buffing wheel rake.