Stone Burrs. The thick, 4" diameter corundum stone burrs of the Wonder Junior mill combine aggressive precision grinding with long burr life. Using the stone burrs, your Wonder Junior can grind wheat (both hard and soft), oat groats (dehulled oats), rice, triticale, kamut, spelt, dry beans, lentils, dent (field) corn, popcorn, dried sweet corn, split peas, buckwheat, barley, rye, millet, teff ...