In addition to the fascia holding the new cage in place, my Sony MEX-N4000BT has a bolt that you screw into the back of the headunit and a rubber stopper that you attach on the back which is supposed to push into the factory radio support. It's a little short but replacing it with the Fiat one from the factory radio makes it long enough. It needed a wind of tape around the bolt to make the factory support stay in place though!