I have tried to remove the air filter box on my Seicento (2002). It seems simple enough (two screws and the spring-loaded clip). The screw nearest to the front bumper came off easily, but the screw on the opposite site (near to the top coolant bleed valve) was just spinning round and wouldn't unfasten. The space is too cramped for me to see what is wrong. Is this a bolt rather than a screw?
Thanks,
Andrew

Exactly the same thing happened to mine it's a bolt that screws into a nut with teeth on to grip the plastic it's sat in, u may have to stick the nut back in to be able to tighten it back up again, try pulling a bit and undoing at the same time it is quite fiddly.

I still can't get the ***ing thing off. I can now see that there is a metal disk that I assume must be the "nut", and this is spinning round when I try to unscrew the bolt. There seems to be no way to get underneath or otherwise at this metal disk to stop it spinning. I have tried gripping it with long-nosed pliers but there is hardly anything to grip and this doesn't work. What exactly did you do to grip this nut please?
Andrew

Honestly can't remember mate I think I just ripped it off in the end.

I got it off. I unbolted the coolant reservoir tank and was then able to get some mole grips onto the "washer" and plastic base that held the threads.
Thanks again.
Andrew