What is the term used for devices used to fasten a prisoner's wrists or ankles together?

The term most commonly used to refer to devices that fasten a prisoner's wrists or ankles together is shackles. Shackles are specifically designed to restrain the movement of an individual by encircling their wrists or ankles, thereby limiting freedom of movement for security purposes.

While terms like chains and fetters may evoke similar images, they have distinct meanings in specific contexts. Chains could refer to a broader category of linked metal pieces, not necessarily designed solely for restraint. Fetters can refer to specific types of shackles used for the feet, often implying a heavier or more cumbersome design but do not encompass wrist restraints. Therefore, shackles is the precise term that encompasses devices used for restraining both wrists and ankles, making it the most appropriate choice in this context.