These end caps are hand carved from Amboyna Burl, one of the most beautiful burls in the world. These end caps are magnetic. We use high quality neodymium magnets that will securely hold your necklace or bracelet. The pair pictured have a 12mm opening, but this item is available in virtually any size. If you need a size not listed here, just let us know - we can make it. Each end cap is approximately 3/4 inch long.