That looks like it should fit. At less than 4 bucks just throw one in your next toy order (I love "shopping" vape gear at FT, you get a bucket of stuff for next to nothing) and try it out. In other words, "reconnoiter and report." (old Navy saying, actually Marine but, we appropriated it).
I received a fasttech order yesterday with two Monster bases. They fit the barrel of the kayfun perfectly.

