Found this at a colonial Site earlier today. Not sure if it is a button, or what. any info appreciated. it's 1 3/4" in diameter. The hook on the back is 1 1/4" long, and 3/8 " tall. A section of it was broke off, when I dug it up this afternoon :-(
I'm not really into the military stuff, so I'm sure someone else will correct me, but from the picture and your descripiton of the piece that was on the back, I would lean toward a bridle rosette from an old calvary bridle. Just my guess.