Width is 5/8.
These keyhole plates are the thicker ones that the screw heads slide into better than the ones a little thinner of the same type.
The #6 x 1/2 & 3/4 inch screws we sell works great to install these keyhole hangers. They require 2 screws for each hanger.
If you purchase with screws, we will supply #6x1/2 zinc plated phillips flat head screws