There is threading on the inside but it didn't seem to fit and I didn't want to force it but I guess it's worth another try. I'd feel stupid note if it does fit lol. About it being a knockoff: that is possible I guess. I am relatively new so I probably wouldn't have noticed. I ordered it from liberty-flights.
Liberty Flights is a forum supplier. They've a section
here. So, no, I wouldn't think they'd be selling knock offs. They'd have gotten the boot from the forum.
You know, with cartos (Blu and otherwise) I sometimes "miss" getting the threads aligned. It's actually a little more tricky than you'd expect for something you just screw in. You shouldn't have to force it, it should screw in easily. But sometimes lining it up takes more paying attention than I keep thinking it should.
Then there's Blu's "quality control". I started with them myself and was major unimpressed. Dumped the kit two weeks in. Maybe fiddle a bit with 'em a bit but, myself, I wouldn't put a lot of effort into anything Blu.
(Okay, I'll give them this much, they got me started and were my introduction to vaping. They just got really annoying and ended up costing as much as smoking! Their cartos are way overpriced. I wanted to like their set up. It's got a real "cool" factor going. Unfortunately, they seem to have spent more time on "cool" than that "make it work" part)