Regardless of whether the stirring elements of the wet grinding or ball mills are constructed as rods or disks, it is still an open question as to whether the reduction in size is accomplished by impact and by attrition between the grinding media, by attrition alone, or by extremly high shearing strain of the carrier liquid. The ball and wet grinding mills of known construction also exhibit in the ground material a broad particle size distribution. Therefore, in the majority of cases where the ground material should have a narrow particle size distribution, i.e. minimal parts of coarse and overly finely grounded materials, the ball mills or wet mills of known construction do not product satisfactory results.