The connection to a CO2 tank is CGA320, for all US CO2 tanks. They differ only by whether the flat faces have a groove in them or not, and whether the tank has a small internal thread or not. With that groove a permaseal doesn't work. And, without the threaded hole you can't screw in a metal permaseal. But, on all of them you can use a sealing washer, either a nylon type material or a thin fiber washer. I reused my nylon washers several times before replacing them, without having any leakage. But, you do have to tighten the nut that holds the regulator to the tank with a big wrench to get it to compress that washer a bit, or it won't seal. Hard fiber washers don't compress hardly at all, but still have to be tightened very tight to prevent leakage. Unless you are a 250 pound, well muscled person, you probably can't over tighten that connection.