Offered here is a 1920 Maine Commemorative Half Dollar. It is graded by PCGS as MS-65 and is CAC certified. The coin in the above pictures is the one you will receive. 1920 Maine Centennial Half Dollar. Maine Centennial Half Dollar Coin Specifications. Designer: Anthony Di Francisci Composition: 90% silver, 10% copper Weight: 12.50 grams Diameter: 30.6 mm Authorization: Public Law 66-199 Maximum Authorized Mintage: 100,000. Maine Centennial Half Dollar Mintage.