U.S. Navy officer's Pattern 1852 waist belt plate, c. 1861-90. Reportedly also a "stock" (generic) plate available for purchase by naval schools, militia, and private groups in the post-war era.
I got it at the Miles Memorial Hospital Annual Rummage sale - 5 full size circus tents full of stuff people donate . I put in 2 days of volunteer work hauling stuff from the warehouse . They let all us helpers buy stuff 1 day before the general public is allowed in . It was on the ''belt'' table . All belts 50 cents each .