I source these in Northern Pakistan and I cut them to fit a Shapton stone holder. There are two stones. One is a red bevel setter of about 400 grit and the other a whitish finisher of about 3000 grit. They’re sandstone in a limestone matrix so they can be easily be refreshed by soaking in vinegar for 10 minutes. Normal use is to soak them in water for 5 minutes (you’ll hear them “sing”). Great for knives and the white one can be used as a lower end of the scale finisher. Fast cutters and they’re what that knife and sword culture has been using for the last few thousand years.