Just like today some designs are so popular they get used again and again in a variety of forms. These large mounts are double-lys, two Fleurs-de-Lys joined end to end. The Lys was so popular that it was not only adopted as the royal flower of the kings of France, but was used in all sorts of decorations.
Mounts like these would be inserted along the length of a belt to add decorative elements. A great place to learn about belt mounts and how they were used can be found at the Rijksmuseum.
https://artsandculture.google.com/exhibit/medieval-chic-in-metal/HwKSigWK2MaHJA
