Looks to be a military button. British? Definitely old. I looked up BIS and couldnt find anything on it at all....could be rare.
Kind of a mystery. If you have information regarding this button and would like to share please do.
No dents. Rust on the back and some wear on the front. Rear loop still exists. SEE PICTURES.
Right around 7/8" in diameter.
Location E1, MER