I have a BCC Mega tank from iSmoka and it's a bottom coil clearo, with replaceable heads. It's awesome I tell ya... 510 thread, fits perfectly on my ego ctwist, and the vape quality, flavor, and production is most excellent! The best part about it is that it's also very easy to refill, replace juices, and clean. I can refill my juice, connect to my ego, and vape in less than 10 seconds! No priming needed, and I definitely don't need any more paper towels and blowing into carto's. It also doesn't leak at all! HIGHLY RECOMMEND IT.