Key hole covers like this one are found on large roll-top desks, as well as others. This one is a used one from a desk of many years ago. It is made of heavy stamped brass. The brass key hole liner extends beyond the back of the plate and will push into the key hole, giving it a lining.
The escutcheon plate measures 3 1/2 inches horizontally and one inch vertically. The brad holes are 3 1/8 inches apart. Brads will be included.