Thank you for viewing. Diameter: Approximately 10 cm Thickness: Approximately 0.9 cm This is from my father's collection, so I don't know the details. For railway enthusiasts. From AI: This is a metal disc called a "token" (tablet), which was used for traffic management on single-track sections of Japanese railways in the past. It was used in a system called "tablet block." It served as a "pass" allowing only the train carrying it to travel on a specific section of track. There are several types of tablets.