Many old trunk and chest locks had this brass piece swinging down to cover the keyhole. Keep the dust out, maybe?
We have two sizes available but in limited supply. See the two styles in the center of the photo?
Small is on the right, large on the left. Either way, these are $12 each, USA shipping included. Part # Lock-6Sm or Lock-6Lg
The small one is 1-13/16″ long overall, the large one is 2-1/4″ long overall.
Has a 1/8″ dia. round brass post on the back – tap that into the hole in your lock plate and then hammer it a few times on the back to mushroom out the post.