That's a female battery threading and male carto threading?
If it is at least 9mm diameter then it likely is either 510 threading or RN4081 threading. So pick one of those to try the cartos and if that doesn't work then try the other.
RN4081 - see
njoy (or your local 7-11 may have some Njoy Npro aka 2-n-1 cartos, Aquavaporcig, Vaporkings.com, AZAmokeFree
510 - Normal 510 is a 3-piece so there are not a lot of orefilled cartos for it. LiquidXpress, Vaporkings.com for some Chinese
juice ones, Volcano ecigs, Apollo Ecigs, and though it is not 510, cartos for the current Blu should fit 510 threading