Trio's also fit 510/306
threading and in an old list of Trio models, old Blu was listed
You could also use a standard resistance 510 atomizer and carts but the 510 atomizer has an external tube with recessed bridge and would make the Blu longer.
306 is an exposed bridge and the carts push on over it and have a recessed small
juice cup
LiteCigUSA.net should have both 306 and 510 attys in standard resistance