It's just a custom top cap by ohman over at this thread. You'll need to send it to him but his turn around is very quick. At least at that time.
http://www.e-cigarette-forum.com/forum/showthread.php?t=436537
The tank is a nano tank from gr-modders but in this set up I put the standard SS ring on it to make it more of a medium size tank.
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