Hard to say exactly with a natural stone, but my fine Arkansas appears to be in the 1200 - 1500 range. They work very well on chisels, knives, woodworking tools etc. They don't work so well on the tougher steels, but on 440c, Aus8, 420HC, they work very well. They will work OK on the the newer steels like 154cm, but are very slow and not a good choice for anything but touch-up work. For touch-ups, they're pretty nice. As advertised, they really do polish the edge as they sharpen - makes for a great looking edge.
HH