no, it's not the filter that came with my x-tra. it was part of the x-chamber - i'm sure of it because when i first got it i was lookin at it. it was on top of the x-chamber where it screws into my vert ASA and i guess the ASA pushed the little metal disk down and allowed the co2 to pass thru, but i dunno. i guess i should just not worry about, just as long as it works.
but if anyone knos wat i'm talkin about, i just want to kno if that was an important and/or necessary piece.