Our 3M 6" "Hookit" Microfinishing Discs are waterproof and ideal for wet or dry sanding. The heavy duty loop backing makes these 3M discs compatible with any 6" random orbit sanders with hook and loop pads. The great advantage of hook and loop is that the microfinishing discs can be reused over and over greatly extending their longevity and reducing your finishing costs. These disks also work perfectly well with 6" sanders lacking dust collection. 30u is similar to 320 grit. They are sold in singles. 6" Six-Hole Pattern Discs fit DeWalt DW443 and other sanders with a similar hole pattern.