FIG. 1 is a perspective view of a rotary grinding stone having a centrally disposed hole according to the new design. FIG. 2 is a front side view of the rotary grinding stone of FIG. 1; FIG. 3 is a right side view of the rotary grinding stone of FIG. 1; FIG. 4 is a rear side view of the rotary grinding stone of FIG. 1; FIG. 5 is a left side view of the rotary grinding stone of FIG. 1; FIG. 6 is a top view of the rotary grinding stone of FIG. 1; FIG. 7 is a bottom view of the rotary grinding stone of FIG. 1; and, FIG. 8 is a cross-sectional view of the rotary grinding stone of FIG. 1, taken at section A—A in FIG. 6.