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 paint, rust, and other materials from metal surfaces. The disc attaches to a back-up pad on an angle grinder and rotates at 13,300 RPM. It should be used with eye and face protection. This made in the USA product can smooth, clean, and condition metal surfaces.