I now have the answer to my own question.A T40 star bit drive.A 6mm allen key will also work but the correct tool is the T40.
Another point is to watch out for the oil filter as my Fiat dealer give me wrong one!There are two types -one has an extension on one side the other type has little castellations -for my 2008 punto grande the castellations was the one I needed.
The tools needed for the oil change are:
a 27mm socket-for the plastic housing
a 10mm socket- for the metal protector
a T30 bit - for the metal protector
a T40 bit (socket type) for the oil drain plug
A straight forward job once I had the tools and filter sorted.