This is an example of the smallest oval door knob back plates. It is actually a rosette. These small plates were used on the backside of the door accompanied with a key hole escutcheon when there was a locking system on the door. Today rosettes are used when mounting door knobs to a board for another purpose, like for coats or jewelry. The rosette gives the door knob added attraction and finishes the décor piece. This rosette measures,4 1/4 inches long by 1 1/2 inches wide. It is small enough it could be used vertically or horizontally. This rosette is from the early 20th Century.