Generally, door knockers have some sort of ring hanging down that performs the knocking motion needed to use the door knocker. The large round rings on the door knockers are sometimes called a door knocker earring. The rings can measure anywhere from 3” to 6” in diameter. The door knocker earring is a decorative ring hanging from the door knocker and it looks somewhat like a “hoop earring”. Door knocker rings can be made of various materials such as cast iron, brass, nickel, etc.