I'm having trouble determining what the part number is for the backing nut that holds the bolt and plastic clip together onto the window glass and regulator. I noticed when changing the plastic clips last fall that I was missing one backing nut...and didn't find it at the bottom of the door interior.

I can't really tell from RealOEM.com. I remember the backing nut having the shape of a flat conical cylinder and not in the traditional hex or octagonal nut. Any help? Thanks.

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2000 Z3 2.3 Steel Gray
2004 X5 4.4i Jet Black