nettles, Kevin and silverbullit seemed to have explained things very well for you.

Since I know you have some Unique
tanks, you'll want the Unique sized ones for those and the standard/Elegance size if you want to use them with Kathy's caps and regular lenght carto's.
EDIT: Just read you usually use the x-long carto's, so the JB size would work for your uniques I would think and the Unique size should work for Kathy's caps...she will check in here later I am sure and she will be able to answer for sure on the sizes.
Great group of people here, so ask any questions you need to and someone will always do their best to answer them for you!! Kathy is super busy right now getting ready for a vape meet she will be selling at, which is only a week away, so I know she is busting her .... right now...poor girl!!!!