Walnut Shell is used as an abrasive blast media similar to sand for cleaning, but without the negativities associated with other abrasive materials. In many typical cleaning applications the substrate is metal, fiberglass, wood, plastic or stone. Walnut shell can be utilized without scratching or pitting the substrate material / underlying surface. The walnut shell is ground to various sizes from coarse to extra fine depending on the application. Walnut shell does not cause silicosis, a harmful lung condition associated with the use of other blast media. Suggested Sizes are 8/12, 4/6, 12/20, 14/30, 18/40, 20/40, 40/60, 40/100.