upper and lower millstones are provided in a milling apparatus adapted to mill a wide range of cereal grains and other kernels . the upper millstone is stationary and is pierced by a central orifice through which the drive shaft of the rotating lower millstone passes . cutting teeth protrude radially from the drive shaft in the region of the central orifice and cooperate with guide channels in the orifice wall to break kernels larger than would pass through the annulus between the shaft and the orifice , thereby supplying pre - milled kernel fragments to the opposing milling surfaces of the upper and lower millstones . radially spiralling furrows in the milling surfaces further reduce the feed to flour , prior to discharge at the outer periphery of the milling apparatus .