Does anyone know the brand of the fuel cap on Fountains (2006)?
I'd say Perko by heart, but not 100% sure....

I found one at west marine that looks exactly the same. The size and thread pattern matches up. On my boat the fuel fill cap is same as the head pumpout cap so I took the head cap to West Marine and matched it up after an unsuccessful guess. I think it was the west marine brand actually that I purchased which turned out to be inexpensive by the way.

Sorry I assumed you were in US but you are in Italy so may need to measure diameter carefully then order online?

I think Hardin Marine makes one CP performance has them in their catalog.

I had to replace mine before. Damn if there ain't a dozen different styles/sizes of them, and just a tad different from each other. The threads was easy, but finding the right size OD cap was the kicker. Ended up finding one close and then machining the cap to fit.
Mine was originally chrome plated, not SS. That seemed to make a little difference as far as the choices.

Thanks guys, I should have guessed that the only way is to match it up against the original one. Which I still have btw, it's just a bit scratched and I was thinking to replace it.
No big deal, I'll wait till the next time I'll be on the boat, to remove it and find a new matching one.
Why on heart they make many slightly different ones, that's beyond me, anyway....!