It seems that lately the vast majority of the bottom coil tanks are using the protank style heads. And a lot of people that use them also rebuild them, including myself.
My biggest complaint about them is that the little rubber grommet often rips apart when trying to get them out. Or you get burn marks on them. But for what ever reason they are just not reusable any longer. So up until now your only option was to purchase another head.
Well I am here to tell you that now there is another option that I stumbled upon when I did a google search. These were originally made for the AGA series of tanks as a replacement. Well as fate would have it they also work in all your kanger and evod heads as well.
I was a little skeptical at first because just looking at the picture they look a little bigger. Long story short. I got some and they work just fine. They take a little more effort to get in but they do fit and fit well. I don't know for a fact but they also seem to be made out of a little better material and therefore should hold up a little better. Here is the link where you can purchase them. http://www.kidneypuncher.com/aga-series-positive-post-insulators-10-pack/#reviews