Inner diameter size: Approximately 5.5cm when laid flat. This is a used item. It was purchased as a ready-made product from a power stone shop. The type of stone, origin, and whether it has been processed are unknown. There are no certificates or instruction manuals. I have checked the rubber by gently pulling it, but please be aware that it may break down due to deterioration. I am not familiar with power stones, but I exposed it to sunlight for purification. #PowerStone #Bracelet #Mix #Multi