Is it a button?

[Tommy G]

I was digging one of my favorite sites yesterday and came across this. It is made out of copper, has a smooth curved lip, and what appears to be a broken shank on the back. My first thought was "button", but I've never seen one shaped like this. Sorry for not putting a ruler in the picture, but it is the size of a Dandy button. This is from a 1756 home site that has remained occupied through the years, so I have found everything from 18th century coins and buttons to modern clad and pull tabs. Had it not been for what appears to be a broken shank on the back, I would have tossed it as junk. I am interested in any ideas.

 

[duggap]

It looks like the back of a two piece button.

 

[Tommy G]

It looks like the back of a two piece button.

Two-piece button was what I was thinking as well. This may account for the curved lip that may have held the other half in place. Thanks for the looking.