Missing Link

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

Other Versions of The Missing Link
Below are the other two sides and end stickers of the Missing Link and Missing Link Deluxe, and the other two sides of the Missing Link keychain (the keychain does not have stickers):

There are other productions of this puzzle; some the same but with different stickers (e.g., one sold in France said "Le Chainon Manquant" on the stickers), as well as ones that have the same dimensions but different colors, different internal construction, or different overall quality. Here are three examples of different ones with English language stickers; for all three, the stickers on the two ends are the same: