The Norton Surface Conditioning Disc is a 4-1/2 inch diameter x 7/8 inch thick Type 27 depressed center grinding disc made of aluminum oxide. It has a very fast cutting action for removing rust, paint, and heavy oxidation quickly. The disc attaches to a back-up pad on an angle grinder, die grinder or straight grinder. It should be used with light pressure at 10,000 - 15,000 RPM for optimal performance. This Made in the USA disc helps prepare surfaces for painting or powder coating.