Authentic GT Core coils are specially designed to fit into the NRG and Cascade tank series. (plus many others)
They comes in different resistances:
GT2= 0.4 40-80Watts – best at 55-65w
GT4= 0.15 30-70Watts – best at 45-60w
GT8= 0.15 50-110Watts – Best at 60-80w
GTMesh= 0.18 50-85Watts – Best N/A
GTCCELL= 0.5 SS316- 15-40Watts – Best N/A
GT CCELL 2 = 0.3 35-40 Watts
GT4 Mesh 0.15 ohm 50 – 75W
Comes as a pack of 3 coils.