MDF spacer rings. I am myself using 6.5" speaker in the rear doors. I will try to find photos and post here as soon as possible. Stock speaker in rear door is 5.25" to be precise but that doesn't mean that the space is not meant for 6.5" speaker. No. Not at all because I am like that too. Everything I am sharing here is on the basis of my time spent on reading up many discussions and guides. When it comes to any upgrade, it is best to discuss it as much as possible. The typo was from me. I mistyped 3690 instead of 3590. You can get these from the place where you wish to install the set up. You can also buy it online in case you plan to install it yourself. Let me share some pics and links. The antenna adapter looks like the following. Image sourced from net as I didn't click pics during installation. Cost around Rs50-150 in local market. The ISO adapter cable looks like the following. It costs around Rs150-300 I guess though not sure. Why do we need this ISO adapter cable?? When we remove the factory fitted stereo, the wiring harness by FIAT is the standard ISO cable that looks like this (look at the black harness cable with multiple pins): BUT, the aftermarket stereo comes with a non standard input pins such as the one shown below (look at the slot on the stereo just above the text 7590): They even supply a cable for it in the stereo box. The black end of this cable goes inside the port meant for it on the rear of the stereo. But look at its other side. There are just wires on that side. These wires can not be connected to the harness present in the FIAT Grande Punto and thats where this ISO adapter harness comes into play. The wires of the harness coming from stereo are connected with relevant wires of the ISO adapter wiring harness and this further connects to the stock wiring harness. I hope the images are self explanatory. I finish the post with the image of a stereo panel.