CO2, N2, or compressed air is what gives your gun the power. There is different sizes you can get these tanks in too. You can get them in 8-20oz tanks. With a 20oz tank you get approximatly 1,100 shots before you need to refill it. There is always a danger level with your power supply so make sure you follow safty instructions you get with your power supply. The small CO2 tanks are made of chromolly and the largers like the 20oz are made of aluminum but the chromolly tanks are lighter. Every CO2 tank ive ever see had a pin valve but i dont know if they are standered or not. They also make 4-12 gram CO2 tanks but you can't refill them.