These are the only ones I use, but I've been having a hell of a time using these cartos in these tanks:
6ML Colored Tube for 510 DCT (Dual Coil Tank)
I don't know if the tank caps have issues, but I bought 8 of them, and not only are the cartos very tight to get into them but the top and bottom caps are also very tight to get onto the coloured tubes. I've tried 3 different tanks so far and they are all the same.
I bought the tanks during the last sale. Anybody else experience this?