I would like to clarify something that Orobus mentioned. He said that the flange that are present on some cartomizers (ie Smoktech) were to keep them from sliding off the tank. Actually, they only keep the tank from sliding toward the battery, not away or off the battery. Once getting a cartotank, make it a practice to pick up your tank/battery combo by the battery only. Although the vast majority of tanks fit snuggly on the cartomizer, don't push your luck by picking it up by the tank only.
The Ikenvape brand carto's are known a standard for the 35mm length, and "Mega" for the XL length, FYI. Additionally, althought DCT stands for dual coil tanks, single coil cartomizers fit and work in these just as well.
I've accumulated a vast amount of information on tanks and cartomizers in my blog articles. I have detailed descriptions and video links, lists of vendors that sell pre-punched cartomizers, what juice carriers are safe to use with tank-cracking flavors, etc. You can find these articles in my blog by clicking the link under my avatar, and then clicking on the article's title to read it.
Good luck. -- Baditude