The GeekVape Replacement Glass Tube is designed for Zeus Dual RTA and Zeus X RTA. It comes with 4ml and 5.5ml juice capacity for your selection. 1 piece each pack. Just get it as a spare part for your tanks!
Please note that when you install the 4ml and 5.5ml tubes to Zeus X, the actual capacity will become 3.5ml and 4.5ml.