Pure is a j109, yet another 510 mini. If you want cartos that sit flush on the e-cig, then you want 8.5 mm cartomizers which are hard to find and rarely cheap due to being over-branded.
Blu, Volcano, Jet, and Modern Vapor all sell j108, j109, l88b and j118 cartomizers so they'll be the same diameter as your battery.
J306 cartos are 8.6 mm I think, so they'll only be slightly larger than the battery.
Anything else 510
threaded may work, but will probably look a bit silly.
I got this info from a 2 year old thread on ECF and E-Cigarette-USA which states that the j109 cartomizers are compatible with Blu. Things may have changed in that time.
Good luck!