It's used wet, in a tumbler, not a vibratory type
Stainless, Zinc, Aluminum and Copper Cut Wire Shot - Pellets, LLC
I spoke with Kevin, who assisted me in ordering the proper size. They are basically short, thin pins which work very well inside and out and clean quite well. I did a bit of shopping around, and this was the one with the best price, $5.00 per pound, with a 5 pound min.