Rivets, solder, and back.
Mounts decorated furniture, belts, books, and boxes. Look at the back for rivets, solder, or integral lugs that show how they attached — the back usually identifies the job the front only decorates.
Belt fittings are their own datable family: strap-ends, buckle plates, and rows of small bar mounts follow fashion closely through the medieval period. Book fittings — clasps and corner pieces — often outlive the book.
Sheet, cast, and stamped mounts belong to different traditions and dates; thickness and the crispness of detail tell you which you have. Gilding and enamel traces in recesses reward a look under magnification.
Record shape, fixing method, and decoration style separately. “Mount, purpose uncertain” is a common and honest entry — the attachment marks will often say more than the ornament.