The 3M Black Belt in size 7-7/8" x 29-1/2" with 24 grit is a heavy-duty floor sanding belt designed for aggressive stock removal on hardwood floors. Unlike the purple 3M Regalite belts which use ceramic aluminum oxide, the 16 and 24 grit "Black" belts typically utilize a distinct abrasive material, often described as looking like "rocks" or using Silicon Carbide or a specialized coarse mineral for rapid leveling and stripping of thick finishes or uneven flooring.