Unlike most jump rings, which are open or can be opened with pliers, solid / closed jump ring findings are cast in one piece, stamped from sheet, or soldered closed.
Popular uses:
simple bails on delicate cording and ribbon, such as silk or rattail (the opening on normal jump rings can snag these delicate materials)
simple bails on braided wire or cording such as Viking knit and Kumihimo
secure connector links for assemblages of dangles
the "other half" of a clasp at the back of a necklace
