Resin backed and last 3 times longer than standard sandpaper. Safe up to 22,000 rpm. Grind and polish castings, port heads, and finish small parts. Arbor hole is 1/8", use only with mandrels listed. When working on aluminum or other soft metals, use Grinder's Grease for a smoother cut. Save by ordering the Tight Spot Grinding Kit or order different size and grits