The Combo RDA is a 25mm diameter atomizer with bottom airflow system. It comes with very innovative spring design deck which is a "tool-less" RDA, that means you don't need tweezers or tools for setting coils on posts, the 24K gold plating allows for greater conductivity. Deep juice wall for more juice storage. The Combo RDA is the perfect RDA for those looking for a simple, fashionable and flavor based RDA! The PEI version: Ultem is a High-Temperature plastic with a significantly higher melting point compared to delrin. Give the Combo RDA a fresh look while enjoying the comfort of these caps.