ok I have the nexus hub prebuilt into the wheel that is sold by Harris Cyclery.

I just figure out that one of the metal circles is really a spring clip, and looks like it is for holding the sprocket in place. There is another black plastic ring that I am not sure where is goes.

Perhaps under the brass colored metal ring?

Ok never mind, simply looking at all of this in the morning, with a well rested brain is working much better then at the end of a really long, stressful day.