You pretty much have to stay within a connector number (510, 901, RN4081,...), then buy adapters (e.g., 510batt/901atty) to cross models. Good prophets sells a bunch of adapters, and I've also bought them at Ikenvape; other places carry them, too.
The one exception that I know of is that KR808D-1 and 901 share the same basic connector, battery side is male, carto/atty is female, same diameter and thread pitch. The 808D-1 just includes slots on the battery-side connector, for air flow. SOme things that are nominally "901" may actually have the air slots to support KR808D-1 cartomizers, otherwise you actually use a 901/808 adapter; the 901/808 adapter can also be used on nominally 808 batteries, as they can help on the connectivity or improve air flow (even some "real" 808 battery-side connectors can have pretty tough draw).