This listing is for one brand new Grey Anodized 6061 aluminum CGA320 nut and nipple that will fit on any bulk CO2 tank valve in the US, 5lb, 10lb, 20lb, or 50lb.  Look at the base of your tank valve.  If you see CGA320, this valve will fit.  The end of the nipple has male 1/4" NPT RH threads. This fitting is used on Paintball fill stations as well as beer keg CO2 tanks. If you have a regulator, you can make your own portable air supply for nail guns, etc.