Möbius Hoop Ring
This ring's band forms a Möbius strip, which is a surface with only one side and only one boundary.
If you move a finger along the flat part of the strip, it will return at the starting point having traversed the entire length of the strip (on both the inside and the outside of the ring) without ever crossing an edge.
If you move a finger along the flat part of the strip, it will return at the starting point having traversed the entire length of the strip (on both the inside and the outside of the ring) without ever crossing an edge.