Collectible coins encompass a variety of types, including patterns and trial coins, which are specially struck pieces that test designs and production methods. In the United States, the 1880 four-dollar gold coins, also known as "Stella," are among the notable collectibles, produced in limited quantities to promote a metric currency system that was never adopted. Patterns and trial coins are often sought after by numismatists due to their historical significance and rarity. The designation "N A" generally refers to coins that have not been graded or authenticated by a professional service.