Ok

Its my plastic clip ( no.7 ).

A very simple design from BMW. Nut 6 sit in plastic clip, when you tighten up Nut 5, it suck nut 6 through which open up the plastic clip arms (which you can't really see on the diagram) which designed to prevent glass from jumping out.

I bought nut number 3 as well but didn't need to use it.

Thank you for providing the diagram.

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13.6 Street tire Gtst
11.6 Street tire R32 GTR