Cognate rings are accessories that Cognates wear on each of their thumbs when performing mind readings. Fitz gave Sophie a pair as a Midterms gift, which were engraved with their initials, SEF and FAV. When Cognates' minds are telepathically linked, the rings snap together, as the rings are made of ruminel, a metal that reacts to mental energy. This helps to "connect" the minds, enhancing their concentration. When Fitz and Sophie's rings snap together, their mental power is stronger.