I don't know why the 808 version has the Ego threads at a smaller diameter than a 510 counterpart. the 808 mega carto doesn't use those outer threads towards the base to attach itself. (Nor does a 510 mega carto for that matter.) I think those threads were originally intended for cone shrouds when using a drip cartomizer. Anyway, I now use my Egos just with the Mega cartos, which are quite nice. Took me awhile to get used to the mega. Tanks go onto mods or 3.5ml I'll use a manual stick batt. speaking of tanks, need more 2.0 ohm cartos. Starting to get that nasty gurgle in some of them.