score:5
The "chape" of a buckle is the part where the buckle is attached to an object like a belt or a shoe:
This was frequently in the shape of a plate for belt buckles, as in the example in the question, and these buckles listed on the metal detecting finds database.
Even when the other elements were missing (as in the famous skeuomorphic "Great Buckle" found at Sutton Hoo), the chape, or plate, would still be present, allowing it to be attached to a leather belt: