A suntetsu is a metal rod/spike about  in length with a ring attached to it. The middle finger is inserted into the ring and the suntetsu rests in the hand by various grips.
A suntetsu is a metal rod or spike of moderate size, typically around  in length, featuring a loop at its end. By inserting the middle finger into this loop, the suntetsu can be comfortably held in place using various grasping techniques.