I don't have a banjo burner, but I think they use the same kind of jet orifice. I used this one from morebeer - it's got pipe threads, not the flared fitting that are typically used with the flex gas lines. Burner Jet - 1/8 in. x 1 in. | MoreBeer
My gas plumbing is all 1/2" black pipe, but you could also use 3/8" if you wanted.
This is what mine setup looks like.