Type of part needed

[Teri]

Hi all just wondering if any of you know what type of tool and size I need to open this nut ..is it a specialised one I can only get with audi them selves..I'm trying to do an oil change on my a7 but can't open these ones? 

I attached a picture below maybe someone has had this same question and know the answer

[cliffcoggin]

It looks like a Torx fastener. They come in a range of metric sizes and are available at most tool merchants.