[QUOTE=ernestrome;89071]The pro stones are full thickness, ie what you see is all sharpening material, whereas the m5 stones are only a quarter inch of sharpening material glued to a ceramic substrate, much like the glass stones which are glued to glass.QUOTE]

Thanks... yup, that's the difference, m5 and professional are the same material, just different amounts of it. I can't imagine ever even making a dent in the m5, let alone an entire stone. I found a great price at epicurean edge... $39.85 for the Shapton m5 12,000 grit. I bought that and a nagura stone for less than $60 shipped to my door. Not bad for such a high grit stone.

Andrew