Alan Cole
This type of clip was used for some four hundred years in two ways. In Byzantine culture for keeping a bound book open whilst the scribe continued to write. However, an English image of 1350 shows them used for keeping a single sheet from cockling during writing. The way they function in keeping a bound book open is to clip together enough folios to provide the necessary weight.
The other use was for picking up a wet manuscript leaf between the plates, pulling down the locking ring and then threading a cord through the loop at the end to enable it to be hung up to dry. It is possible that two such pairs of tweezers might have been used in conjunction to keep the leaf flat and stretched while drying.
This item is missing one plate.