Additional awards of the Air Force Overseas Service Ribbon are denoted by oak leaf clusters and Air Force regulations permit the receipt and wear of both the short and long tour ribbons simultaneously, wherein the short tour ribbon takes a higher precedence by being worn to the wearer's right of the long tour ribbon. The "A" device is authorized only on the short tour ribbon to any service member who performs a tour of duty at an arctic based Air Force facility; most commonly Thule Air Base in Greenland.