Alc 40112 20 grit black walnut shells – 10 lbs. 10lbs medium, 20 grit, 0.053″, 3.0-4.0 mohs; used for cleaning and surface preparation of soft metals, glass, chrome, fiberglass or hard wood surfaces where no pitting is desired; typically used in a blast cabinet or where the abrasive is being recycled; can also be used to remove graffiti from most solid surfaces; note: the size of the blaster nozzle should be three to four times larger than the grit size of the abrasive being used, the larger the nozzle the more cfm of air is required