Rear wheel: Where does the this part go

[bigcanoe]

I took my rear wheel off to change the tire. The part with the sprocket attached fell out of the spoked wheel. There is this silver solid metal bushing part. I am not sure where it goes? Does the small tube slide into the center of the piece with the sprocket? Is it sandwiched between the two pieces? I found a parts diagram but couldn't figure it out...

 

[bigcanoe]

It may be #5

 

[bigcanoe]

Ah, I found a youtube video that shows the rear wheel removal and I found out where my mystery part went. There it is, in the center of the part he is holding. Spacer! For reference:

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