Vintage metal thimble. I use it when sewing to protect one of my fingers so that at least one finger survives my attempt to return a button to its proper place. In medieval times very poor knights wore thimbles like this during jousting tournaments in lieu of much more expensive full body armor. Sometimes the protected finger was all that remained of the knight after the tournament ended and the widow would bequeath it to The King. This eventually became known as "giving The King the finger" - a tradition that continues to this day in a somewhat modified form.