On the bottom of the forum banner there's a link to ePER. It's the FIAT spare parts catalogue. In the center of the screen you can find instructions how to use ePER. The search windows is top left of the screen.
You can browse by models and categories or search directly with the VIN number of your vehicle. If you use the VIN, ePER will by default display only the parts compatible with your vehicle. Browsing to the correct category you will have a diagram on the left, and a list of part numbers on the right:
Clicking the part number will lead you to the description of the part:
On the bottom, when you click the 'Drawings' button, you will get the list of all FIAT vehicles in which this part was use::