Since you'll be affixing the metal cup to the plaque with a nylon tie, drill holes in what's roughly the center of where you cup and plant will sit; make these two holes about 1 ½ inches apart ...

John Henning, Jr. Large metal relief plaque designed for the upper cover of a bookbinding. 1822. Attached to a folio album with blank sheets. Graphic Arts GAX 2010- in process. The Scottish sculptor ...