A type of brooch in the form of a complete ring to which is usually hinged a horizontal pin slightly longer than the diameter of the brooch. The point of the pin rests on the ring opposite the hinge, and the brooch is worn by pulling the fabric up inside the ring, passing the pin through it twice and then drawing the fabric down so that it hold the pin in place.
In some examples two short pins extent from the ring to a centre transverse crossbar. Such brooches were used frequently in medieval times, and examples have been found in hoards of buried Anglo-Saxon jewelry and also among English jewelry of the 13th/14th centuries. Most specimens are plain but some are decorated with inscriptions or gemstones set around the ring.
From: An Illustrated Dictionary of Jewelry, autor: Harold Newman, publishers: Thames and Hudson