The (insert random use, not related to actual intent)Shell is Atmizone’s RBA bridge concept for Billet Box rev4 Boro tank and compatible tank systems. From loose lung hit to MTL, it will suit your (insert random use, not related to actual intent) habits, with the classic air flow pins and air flow control ring included out of the box. The optional purchase of MTL Air Flow Pins Kit allows a true MTL experience, extra precise and with no need of AFC Ring adjustment.