This Air Force Challenge Coin is finished in polished nickel and is engravable with 2 lines of text - up to 11 characters top line and 8 character on the bottom line. Honor your service or someone else with this personalized coin. Dimensions: 45mm diameter, 4mm thick. This Air Force Engravable Challenge Coin is the perfect addition to your military coin display case! Medals of America has all of the USAF challenge coins for your collection.