Aluminum Oxide Grinding Wheels are the accepted standard for sharpening high-speed steels and high carbon steels, as opposed to conventional grey, hard, slow cutting wheels, which tend to burn tools as the grinding surface becomes dull and glazed. Our Norton Aluminum Oxide (AO) White Wheels are made of granulated aluminum oxide with a vitrified white bond that permits the grains of abrasive to wear off, thus providing a consistently fresh grinding surface. Sharpening is faster with less danger of taking the temper out of the tool. This 8"-diameter, 150-grit wheel comes with bushings to reduce the arbor hole to fit 3/4" and 5/8" shafts. 8"-diameter wheel is also available in 60-grit (163280) and 100-grit (163281).