The robotic arm contains two of these parts. One is the base of the robotic arm that allows 360 rotation in one plane. An attachment to this part of the arm allows vertical rotation. The second part attaches here and consists of an arm with a perfectly engineered hook. It is practically a modern marvel.
Third picture is the hook.
The point of the right is used to pick up the rings. It sides down the curve and lands in the slot in the bottom. The wave shaped hook in the back holds the rings from bouncing or sliding out of the hook when the arm is lowered to pick up another ring. With a spring attached to the arm to help pick up rings, this whole system has operated smoothly with six rings on the hook. Another functioning part makes up the very intricate and devilish blocking arm.