Hi, Sandie. Hilti is the trade name/brand of gun and it uses a .22 caliber charge to force nails into concrete. I believe that the company is headquartered in either Switzerland or Luxemburg but they market heavily in this country, almost exclusively to professional tradesmen. You should find a Hilti sales group in most big cities and many retailers. Any of them should be able to give you exact nomenclature from their literature or you might find more on the web now that you know a little more for your search.