Standard barbeque quick disconnect natural gas hose and connector. Bought and used a couple times, but eventually upgraded to a larger diameter hose to make sure hose diameter wasn't limiting running 3-BG14s at once. Not convinced it was, but I might as well keep the larger diameter.
The exact one:
$30 shipped, or $20 pick up in Poway, CA.
Edit: I should note that homedepot says it's .5", but I think that's OD which isn't really what most sites use to measure Nat gas hose.
I believe the equivalent kit would be: