I've never seen this gas cap before... is it the normal one for a Demon? I don't know, it wasn't on mine
A couple of other Demons that I posted before don't have this gas cap: http://justacarguy.blogspot.com/2009/03/72-dodge-demon-built-by-aaron-at-viau.html and http://justacarguy.blogspot.com/2008/05/coolest-demon-ive-ever-seen.html
