Still new here. been using cartomizers for first 28 days. Ordered 901 and 510 refill cartridges. THEY LOOK THE EXACT SAME TO ME. Are 510/901 Cartridges the same? Not cartomizers, cartridges? p.s. it is possible I suppose that they sent two boxes of the same thing by mistake cause the little boxes aren't marked. Will post a pic if need be. Thanks for all the help ECF.