(Pack of 20) Brass (Cast) Round Rings (Circular Rings) Outer Diameter: 18mm x Inner Diameter 13mm Thickness 2.5mm Gold Brass Brass "Round Rings" made of brass (brass) Very convenient as a connector (joint part) for keychains, wallet chains, etc. Material: Brass (Cast) Outer Diameter: 18mm x Inner Diameter 13mm Thickness: 2.5mm Since it is not brazed, it can be opened and closed using tools such as pliers.