I must agree with Eddie on this one. The image you sent me reminds me of a Screwback Collar Disc from WW1 or WW2..I'm leaning more toward the WW2 era because of the Small triangle pieces on the outside of the Disc. Most of my WW1 discs I have found don't have that feature on them. Just a screwback. Awesome finds for sure. I bet there are more where that came from.
A belated "welcome !" If you don't have any reference books at hand, this link to an Encyclopedia of United States Army insignia and uniforms has some really good info on Infantry, Artillery, Cavalry, Medical, etc. collar disks & insignias going back to the late 1800s. It doesn't have all of them but will probably give you a grasp of what you have ... or will find down the road.