You don't even have one to look at? The part number is 90178-A0005 about $1 at the dealer. I could take a guess and say the thread is M6x1.0 10mm head.
No I do have one to look at, what I wanted to know is what size the nut was so I can get the correct size wrenches before I start disassembling it. Thanks for the information 71Corolla it's greatly appreciated.