Made of high hardness emery, which is a hard, coarse mineral, making it a fine natural abrasive for metal stripping and scaling for deburring. They make sharpening an easy and efficient task. Package includes 6 pieces 3x4mm, 3 pieces 3x4.8mm, 3 pieces 3x5.5mm replacement stones. Can be used to sharpen the chain of gasoline and electric chainsaws. This makes sharpening much easier since you don't need to disassemble and assemble a new chain, you can sharpen your chainsaw like new in just a few minutes .Using a sharpener to sharpen your chainsaw chain will cut wood with less effort because the chain will make a cleaner cut with the sharper blades.The sharpness is very good and the sharp chain cuts quickly and relatively straight. A sharp chain will extend the life of the chainsaw engine.