True penannular brooch has a sliding pin to catch & clasp a heavy and/or loosely woven wool shawl or tartan. Note that the pin is very thick, like a knitting needle; it cannot be used on a dress or other regular weight garment. The cast, silver toned metal (likely pewter) sports a ram’s head design on each open end. Pin is unmarked. A good set of images showing how to use this: https://www.abbyhook.co.uk/brooches/436080_how-to-wear-a-penannular-brooch.html The circle measures about 1 5/8 across, with the pin extending a little further. Great for reenactment or period costume! Silver Celtic Penannular Brooch, Cloak Tartan Plaid Shoulder Clasp, Ram’s Head