two items found in field same field

[jrwill56]

what is the small square brass piece? It is 1/4 inch Square with a stud on the back. there was a Civil war camp here.
, maybe some sort of decoration

 

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[bowwinkles]

Overall pocket corner rivet heads.

 

[ANTIQUARIAN]

What's on the front of the round disk?
You may have found these two pieces together on the same site, but I don't get the impression they're related?

Dave