Approx. 2 inch Challenge coin -- rough shape.  Can  use small package shipping.  History of Challenge Coins: The challenge coin surfaced during the World War I era. The practice of caring a coin designed specifically for a unit was popular with the Air Force and Army Special Forces. An Individual would carry the Coin at all times and present it to prove affiliation with the organization. These are also used in bars. If someone presents you their coin and you do not present yours back to them, tradition is you buy them a drink.