Patented in 1981 by S. Hanson and J. Breslow.
(plastic, 1.5 inches square by 5 inches long;
deluxe version has same size / end labels / directions, and
although photos do not show it well, it has chrome rings on all sides;
keychain version is plastic 5/8 inches square by 2.25 inches long)
A piece can slide into the empty slot and the puzzle can twist at the end sections, but not the middle. It is easy to solve the yellow and green columns (or any two of the non-white colors), and then the red and white can be solved without disrupting the already solved columns, where the basic operations are cycling 5 pieces (all but the top of one column and the bottom of the other or vice-versa), or cycling 3 pieces at one end of the puzzle or the other.
This puzzle is harder than a 4-high Whip-It Tower because you can't rotate at the center (solving the last two columns by cycling pieces is more like a 3D version of the Fifteen puzzle).
Below are the instructions that came with it:
Further reading:
Jaap's Page, from: http://www.jaapsch.net/puzzles/missing.htm
McFarren's Page, from: http://www.geocities.com/abcmcfarren/math/rdml/rubmlk0.htm
