Sprocket carrier nuts

[Two dogs]

I have just put a new chain and sprockets on the S2R
I also purchased some nice new black nuts for the sprocket carrier.
It was getting near the end of the day and decided to get some advice .
I am running an MPL quick change unit , when I cracked the nut for removal
what looks like the cush drive starts to spin so the nut wont come off.
What am I missing ? Probably something really simple but fading light and
time for beer so left it for some DMF advice.

Also anyone have a link to where I can get some Ti fixings for the sprocket carrier.
Cheers 

[ducpainter]

You have to remove the sprocket carrier and use an allen wrench from the back side.

Not sure of the size...12mm maybe.

[Two dogs]

Thanks you are correct 12mm
off to borrow one.