With the new generation of edge tools becoming harder and containing alloys which make them tough to grind.The Tormek Blackstone silicon SB-250 is designed for hard materials and fast sharpening. It delivers fast steel removal on HSS and exotic alloys and can 'touch up' tungsten carbide. The key to removing material efficiently at low rpm is very sharp grains with high hardness and relatively fine grit size. The SB-250 is made in the same grit size as the original Tormek grindstone and can be graded with the stone grader for fast material removal or fine surface finish.