The only difference I could see between the two versions at FT is that the A version has an extra spare glass tank with it. That's why I ordered that one. Strangely it cost a little less than the B version.
Good to have your experience with gearbest shared. I will try O-rings. Yes, threading with my 22mm is a total mess while 21 mm is smooth as butter. Is the fasttech B vesion fine? I guess you mean $20.10 GEM Styled RTA Rebuildable Tank Atomizer - 5ml / stainless steel + glass / 21mm dia. at FastTech - Worldwide Free Shipping .The B version from FT is different then the one Gearbest sells, the first listing from FT is same as Gearbest, and the same one you & I both have. Mine does not have any sort of o-ring on the chimney either, and it works fine, I've had no leaks. my 22mm ring is just fine, is your threading messed up? I noticed it is quite fine threaded and takes a little fiddling to get it started.
As for the 510 pin, mine could due to be a little longer, but it works fine, I added a couple o-rings on it to stabilize, and prevent it from turning in when screwing it on a mod.
Good luck on tickets with gearbest, my last experience with customer service was about 3 weeks to even answer, then a few weeks between each response.
has anyone tried this one yet? GEM Silver 5.0mL 22mm RTA Rebuildable Tank Atomizer
Yes that would be the one you do not have, I'll probably order one in the next few weeks, going to wait and see if I can catch it in stock, or ships next day status.
Sorry not sure on the size, though I would guess 2x1, I have a big box of extras from spares included with atomizers, that is where i get most of mine.
As an alternative you can use a rubber insulator from a protank type head if you remove the hard plastic one, at least until you get your others.