The 90 gram CO2 tanks by Air Venturi are a necessity in providing plenty of shots before needing to exchange cartridges. Purchasing these tanks in two packs allows you to be prepared with a spare, when you loose track having fun shooting. Works with ALL 88 g CO2 Airguns (e.g., Hammerli 850, Umarex EBOS, Beretta CX-4 Storm, etc....) Features: Pre-filled Disposable Contains 90 g of pressurized CO2 Two-Pack by Air Venturi