Vaporesso GT Coil Heads are specially designed to fit into the NRG tank series. 3pcs in a pack.

GT2 0.4ohm  40-80W, best for  55-65W. 
GT4 0.15ohm  30-70W, best for  45-65W. 
GT6 0.2ohm  40-130W, best for 70-90W
GT8 0.15 ohm  50-110W best for 60-80w
GT Mesh 0.18 ohm 50-90W