These cartridges (also called cartomizers) are at the heart of the eCig system. The cartridges contain various amounts of nicotine (menthol or regular) so that you can monitor the amount you are intaking. 

One pack contains 5 eCig cartridges which is roughly the equivalent 8 packs of cigarettes. So this 3 pack provides you with about 2.5 cartons of Cigarettes. You can choose your desired nicotine strength from 0mg, 6mg, 11mg, 18mg, 24mg or 36mg. 

Start at your current strength, and you can gradually reduce the amount of nicotine to little or none.