Thank you for viewing! This is a keychain designed after John von Neumann, a Hungarian polymath who influenced mathematics, physics, engineering, computer science, economics, game theory, meteorology, psychology, and political science, and a genius in 20th-century science. It can also be used as a necklace by attaching a chain. If you would like to purchase multiple items for a pair or a group, please let me know in advance. We offer a discount for multiple purchases. *Please note that we do not offer discounts for single purchases. Size: 26mm Frame: Silver *The 500 yen coin is for comparison and is not included. We also create original keychains with your preferred designs, photos, marks, logos, crests, people, landscapes, etc. We offer free image creation, so please feel free to comment if you are interested.