Made of high hardness emery, which is a hard and coarse mineral, making it a fine natural abrasive for metal pickling and scaling for deburring. They make sharpening an easy and efficient task. The package includes 6 pieces of 3x4 mm, 3 pieces of 3x4.8 mm, 3 pieces of spare stones of 3x5.5 mm. Can be used to sharpen the chain of petrol and electric chainsaws. This makes sharpening much easier since you don't have 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 sharpening is very good and the sharp chain cuts quickly and relatively straight. A well-sharpened chain will prolong the life of the chainsaw motor.