a.k.a. Moving Beads, Tiger Cross, Wizzard Wedding Ring
Old design, these made by J. A. Storer, circa 1990.
(brass with nylon cord, both rods 9/16 diameter by 5.75 inches long)

This is an example of a moving bead puzzle (e.g., see Coffin's Puzzle Craft book). To solve, pull out the loop and move one ring through the loop and off to the side, pull the whole knot through the hole, pass the ring through, pull the knot back through, move the ring back through the loop and adjust everything to be centered again. This puzzle is often made to look more confusing in a way that does not change the solution, such as making the rings large enough to pass over the rod (first puzzle above) or adding extra hardware (second puzzle above, whether or not a bead can pass through the extra ring does not matter).