Reciprocating pistons put a glaze on cylinder walls & this can stop new piston rings from bedding in affecting both compression & oil retention. Cylinder hones remove the glaze rapidly with the aid of your drill. Smaller hones can be used to de-glaze brake & clutch master & slave cylinders. This Small Cylinder Hone (50-170mm) comes with 4 long medium cut stones. 3 Other Engine Cylinder Hone Sizes: 48-800mm, 19-55mm & 19-60mm.