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 1/8in. use only with mandrels listed. Note: different sizes and grits available. 80 grit (coarse), 120 grit (medium), 240 grit (fine) 320 grit extra fine. When working on aluminum or other soft metals, use Grinder's Grease for a smooth cut. Save by ordering the Tight Spot Grinding Kit or order different size and grits individually from chart.