Delta sanding sheet from Fein. The grit particles, contained per square millimeter in the product, amount to K120. The higher the number of the sandpaper, the higher the density of particles per square millimeter. So, in small numbers (e.g. 24, 36, 40...), we have few large diameter particles that make them ideal for quickly smoothing rough surfaces, while in large numbers (e.g. 180, 220, 320...), we have more particles with smaller diameter that are ideal for intense sanding and smooth finishing. You should also know that sanding with a sander has a much greater effect than by hand. The package contains 50 pieces.