An ingenious device - the purpose of which was to control the prisoner's movements. While being transported from one location to another, the prisoner's neck, leg or arm was inserted into the center of the ring, past the spring. In this way, the jailer could push or pull on the attached pole, resistance was met with numerous sharp spikes in the skin.
Trivia & Comment
The principle was somewhat like the devices called 'Chinese Handcuffs' or 'finger cuffs'.