This is an officer's private purchase sword belt plate without a silvered wreath. This particular plate was among the effects of an officer of the 11th N.Y. Cavalry.
Enlisted men's plates were government issued and are less detailed. These plates are worn by enlisted men who carried swords, such as cavalrymen and field artillerymen. The wreath on enlisted men's plates were made of applied German silver. Some plates made by the Alleghany Arsenal were made with both the wreath and eagle sweated on a cast plate. Recovered plates are often missing their wreaths due to oxidation.