Rappel rings provide a smooth metal surface for the interaction between rope and rappel anchor. These rings have nice large radii for an easy retrieval. The stainless steel ring is the burliest for high traffic locations. The aluminum Cypher ring is light and will hold up well except where the canyon is expected to be sandy - meaning, they cut fairly quickly by sandy ropes. Rapid links are used for this same purpose and are more commonly carried because they can be opened.