[77newell]

Having pulled 16 airbags from my coaches I have never seen construction like it is presented here. On mine, the bottom plate with the single stud is integral, or seemed that way, to theair bag unit. The "piston" as I've understood it is a rubber stop to prevent the bag from totally collapsing and damaging stuff (this is based on Firestone manuals).

I'm inclined to think the bag assembly has failed, the bottom dropped out. I'll check a spare bag in the next few days to see if I can replicate your two part assembly. In the meantime, it's probably worth your while to peruse the Firestone manual and verify how yours is constructed.