I'm thinking about getting a 306 atty for my eGo but the options I'm finding from vendors are pretty cryptic. Some have pictures that look exactly like a 510 atty (no exposed bridge) while others appear to have an exposed bridge. Is it some sort of sleeve that comes on and off? Also, someone on this forum mentioned a 306 "cart." Is there really such a thing as a 306 cartomizer or were they referring to the atty? Sorry if it's a stupid question, lol.