So, I have a smoke 51 trio that I got stuck with off a free trial. I also have a dead njoy npro, which died a glorious death as my first e-cig. I must have charged that thing 20 times a day for two weeks. Anyways, on to the point. After the npro bat died, I purchased a nicotek metro, which I used the leftover cartomizers from the npro starter kit on. They worked. Threads fit perfectly. However, the npro has 4 vent holes around the rim of the bat. The metro has only 2. The 51 trio also only has 2. The cartomizers from both the metro and the npro do not fit on the 51 trio. The 51 trio came with an atomizer and cartridges. The threads are smaller in diameter on the trio than the metro and the npro. All three of these are said to supposedly be RN4081 models. Weird how the trio isn't compatible, isn't it? Is it possible that smoke 51 trio's are made in a custom manner to prevent part exchange? Any feedback would be greatly appreciated. 