GeekVape Zeus Dual/Zeus X Replacement Glass Tube by GeekVape is designed for GeekVape Zeus Dual and Zeus X RTA. It features 4ml and 5.5ml E-juice capacity. It is easy for clean and replace. 1 pc each pack. Just get it for your RTA. Please note that the replacement straight glass tube for Zeus Dual RTA is 4ml, for Zeus X RTA is 3.5ml. And the bubble glass tube for Zeus Dual RTA is 5.5ml, for Zeus X RTA is 4.5ml.