Made by Mariusz Dabrowski, 2007.
(plastic, 1.5" square, 3.8" long)
Custom made by replacing the double center portion of a standard Missing Link puzzle by a single section. This makes a puzzle equivalent to the (much easier) 3-Section Whip-It Tower.
Has solid ends with no holes or exposed parts (so stickers are not required on the ends to cover anything up) and a very smooth click-stop action. Here are the other two sides: