The different thicknesses/hardnesses of the non-woven material are colour-coded: W (soft) = grey, MW (medium-soft) = light blue, MH (medium-hard) = dark blue, H (hard) = red.COMBICLICK Unitized Disc - 5" Silicon Carbide, Fine, Medium-Soft 5PK Recommended for work on larger surfaces on components made of stainless steel (INOX).