This package includes 12 pieces of sanding sponges. The sanding blocks come in 6 different grit specifications: 60, 80, 100, 120, 180, and 220. The lower the grit number, the coarser the grit and the higher the polishing efficiency, but the rougher the grinding effect. You can use coarser grits for initial shaping and finer grits for finishing. These sanding blocks are suitable for a variety of applications including sanding putty, woodworking, furniture polishing, metal derusting, and primer polishing. They are designed to work on both flat and irregular surfaces, and can be used wet or dry. The sponges are made from high-density foam and brown corundum, ensuring durability and resistance to tearing. They are washable and reusable.