Made of high hardness emery for durability Emery is a hard and rough mineral, making it a fine, natural abrasive used on metal for stripping and rust removal to remove burrs. They make sharpening an easy and efficient task. Assorted SizesPackage includes 6 pieces of 3 x 4mm, 3 pieces of 3 x 4.8mm, 3 pieces of spare stones 3 x 5.5mm. Can be used to sharpen saw chain on gas and electric chainsaws. Makes Sharpening Easier Since you don't need to remove and assemble the new chain, this which makes sharpening much easier, you can sharpen a chainsaw like new in just minutes. Keep your chainsaw cutting efficientlySharpen your chainsaw chain with the sharpener, it takes less effort to cut wood because your chain will make cleaner cuts with sharper blades. Sharpens well and extends the life of the chainsaw motorSharpens very well, a chain cutting edge cuts quickly and in a relatively straight line. A well-sharpened chain will prolong the life of the chainsaw motor.