Never heard of assigning grit numbers to leather strops but obviously somebody does. That said, I don't think it makes a hill of beans difference in everyday use and would just ignore what I would consider techno babble. Use what ever good grade of leather that you fancy. The second strop material can be webbing, canvas, linen or hard wool felt. All are used every time before you go to the leather to prep the blade for the leather. My usual routine is 20 round trips on hard felt or linen, depending which strop I use, followed by 60 round trips on leather. To me the choice of which type of leather to buy and which type of material for the pre strop is just personal preference, they all seem to work. The debate about which works best is another version of the Nikon vs Canon debate/flame wars.

Bob