The Flow Tank by Wotofo is a 24mm diameter, threaded top fill system, capable of holding up to 4ml ofE-Liquidand an included capacity reducer that allows the tank capacity to be reduced to 2ml to be TPD compliant. The Flow Sub-Ohm tank utilizes the Wotofo's Flow Coil Family and comes with two 0.25 ohm coils rated for use from 35 to 60W. Additionally, the Flow Sub-Ohm Tank is compatible with SMOK TFV8 Baby Beast Coils (sold separately) for more versatility. Airflow enters the tank via dual adjustable bottom airflow with airslots measuring at 12mm by 2mm each, that can be fully closed. With its simplistic design and replacement coil versatility, Wotofo's Flow Sub-Ohm Tank is a great and affordable sub-ohm tank!