Bloog is currently KR808D-1 threading
Vapor4Life is KR808D-1, and so is Smoketip. And I think (not sure) that Cig2O and Cig2Go may be KR808D-1
And you can buy blank KR808D-1 cartomizers
There is an almost identical looking model some other rebranders have that is incompatible kR808D-2
Note - you are getting auto batteries (because that is all Bloog sells) and autos are somewhat more in danger from juice leaks since they are totally dependent on a drag switch right inside the hole in the end of the battery. Leak enough juice there and the switch will stop working right or the battery could die. So always take a carto off the battery when adding liquid. I also do not really recommend the carto condom method where you push juice in blind. I recommend popping the cap and seeing where you are filling and cleaning it up well.
Vapor4Life has the most prefilled cartos but again - pricy shipping ($6 or 7). Definitely sign up there (lower left) so you will get sale notices. I mainly buy during sales and they have some excellent sales, often near holidays or large sports events.
Re 510 - totally different threading, not even the same gender. The most popular ecig threading, used on the most fat battery models and mods, has the most stuff (widest range of atomizers, blank cartomizers, tanks). What is deos not have much of at all is prefilled cartos