I had one like that, the HA version. Same 3 knurled rings.
I forget the other brand that was making Surefire extenders, I don't think that one is a "Leef" (is there a little maple leef engraved on it anywhere?) ... maybe the same brand that was making the combat grip "detonator" extenders. G&P? Anyway, it's a non-Surefire-branded single CR123 extender. I think Lighthound (a moment of silence.... ) was selling them.
Surefire has a few extenders, A19 and A21 are the most commonly searched for to add a 1xCR123 extension (although I think technically the A21 existed so you could add an A21 and an A19 to an LU collar and make a 6P?), they also made the A/AN-14 to make any of the 6-volt lights to their older proprietary rechargeable series- these are about the length of a single AA.
This looks like LEEF or TNC, I've been hunting for a detonator for a few days now.... nice looking adapter right there!