Black Wrought Iron Coaster Holder for Round Coasters. Thirstystone Wrought Iron Coaster Holder will hold round coasters that measure 4” to 4.25" 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.