Designed and made by E. Pap, circa 1982.
(left: plastic, 3.1 by 6.8 by 1/2 inches,
right: plastic, 3.1 by 6.7 by 5/8 inches)

E. Pap made a number of designs in the early 1980's for generalizing the standard Hungarian Rings puzzle to three rings, two of which are shown above. Although it is not hard to see that they have been custom made, they both work quite smoothly. On the left is a straightforward generalization, and the one on the right is a "half-blind" version where one can only see half of the puzzle at a time and has to flip it over to see the other half; here is the other side: