These grinding-wheels are particularly suitable for the finish of hard materials. They are available in fine and medium grain. Recommended periphery speeds are the following: 1-5 m/s for the fine grain(911) 3-15 m/s for the medium grain (912) The watering liquid used for the cooling and the cleaning is the petroleum, the cutting oil or some types of emulsions. The straightening is done on the grinding-wheels set on runners with diamond grinding-wheels, with diamond powder straighteners or with DEBORIT sharpeners. The grain, to be chosen from 50 to 500, depends on the more or less coarse desired surface. The monograin diamond straighteners are not suitable. The clean maintaining of the grinding-wheel is made easier by the application of a felt-pad soaked into petroleum. If not contrarily mentioned, the finish grinding-wheels are delivered with metallic sockets.The grinding-wheels can also be delivered with angle.