FN Rush Ti question

Got an issue with the FN Rush mounting that I'm hoping the hive mind can help with. A buddy bought one without any research because he liked the aesthetics of the can.

As far as I can tell, it looks like the included piston doesn't have a shoulder to interface with the barrel shoulder but rather it has a taper. Looking at pictures of the factory threaded 509 barrel, it looks like it has a taper. Unfortunately, he doesn't have a 509.

I tried replacing the whole booster assembly with a Liberty thread pitch direct mount, but that didn't work. Next I tried a SilencerCo alpha 3 lug mount and that didn't work either.

Does anyone know what the thread pitch/diameter is of this suppressor? Or if any brand's mount works with this?

I know fn sells a direct thread and 3 lug mount, but he was really hoping to use this on his pistols so he's going to find a standard style piston assembly.