Lord couple of things I have found, although those cartos that come with the tank let the tank slide up and down there are other DC Cartos that I have without the flange that fit much tighter, I'm running 2ohm DC Carto's in my tanks when I use the DC Cartos, no leaks, not a drop. Also you can simply take a pip cutter and cut the tube down to 1-1/4 - 1-3/8" and a Boge carto will work fine in these, so will a Fusion carto, I think you could even run a resorector 1.7ohm ss carto in them at the stock size. For some reason or other the cartos that come with the flange from what I have found are a thousandth thinner then regular DC Cartos so sizes vary a bit in tubes. Either way though there are numerous ways to run different types of cartos in these tanks with very little modifications to none at all. Just want to touch on these things a bit. If you get tricky you can also run an Atty in them as well