It was a light brown coloured plastic nut.
So naturally I had a fiddle. It seemed to be spring loaded, If I pulled it up it would unscrew. So I unscrewed it and now it wont go back on.
underneath this nut was a pin type thing, a spring and a sleeve.
I have taken some photos to help.
Dont mind the spilt coolant, Ive just been changing pipes.
Cheers Guys
Nut sat where it should attach

How it looks not fitted with pin, spring and sleeve in.

Nut

Pin, spring and sleeve

