Black Wrought Iron Coaster Holder for Square Coasters. Wrought Iron Coaster Holder will hold 4 square coasters that measure 4”. diameter. Our wrought iron coaster holder is decorative and functional. Coaster Holder is designed to keep your coasters organized and out of the way when not in use. Wrought Iron is a type of iron that has been heated then hammered and molded into shape. Wrought iron is known for its durability, strength, and distinctive appearance.