I’ve been detecting a 1850’s 60’s fort. I’ve found eagle buttons, arrowheads, bullets and personal items. I found this item. I’m not sure what the purpose of it would be.
No question in my mind that it is broken. Based on size and the nice, clean hole drilled in it, I'm guessing it is part of a field made button. Note that the "teeth" around the edge are not uniform. Also pretty confident the hole was drilled after the item was cast.
Lay the item on a piece of paper and trace the arch. Then move and continue to trace until you get a circle. Is the size consistent with a button from the era?
I've snapped/broken buttons like that where they fasten my suspenders to the back of my reenactment/living history trousers.