These are definitely original US Military manufacture. But, the problem is with the identity. These are being sold as US bridle rosettes and sometimes labeled as US bit bosses, but they are not in any way associated with cavalry!!
They are actually the brass medallion that went on the .45 - 70 Trapdoor bayonet scabbard. Another case of mistaken identity. See examples below:
Several crates of these were discovered that were left over from the manufacturer. The Federal government has always produced more than what they need at times. Upon discovery, these were sold and distibuted widely. They pop up everywhere.
Easily identified by the elongated, sometimes squared, brass studs on the reverse. Rosettes would have an iron loop. Bosses would have rivet holes for attaching to the bit.
Here are the standard sizing and dimensions for an ORIGINAL M1859/63 bit boss. Note the textured backgroud of the field behind the US as well as the overall design:
* * BEWARE * *