Kasumi Combination Water Stones help keep the edges of your knife’s blade razor sharp. If your blade edge is in bad condition, start sharpening with the #240 rough grit of the water stone. If your blade is in average condition, start with the #1000 medium grit. These two grits will keep your knives sharp enough for normal home use. When the stone get uneven, use the included flattening stone to smooth its surface for optimal sharpening.