Cog

A Gear was a block that was leaked and was supposed to be added to Indev, but never got added. Its data value was later replaced by the Redstone Dust block in an Infdev update. Gears were first seen at this point of this video, being placed onto the wall of a cliff. A Gear's sprite consisted of two parts; the center rod and the animated gear.

Gears could only be placed on a side of a block, placing them in a space where two sides are next to each other would cause two Gears to appear on both sides. Gears did not do anything and could not be obtained without hacking one's inventory. Placed Gears were impossible to destroy; any mining directed at a Gear phased through to the block behind it, much like Water. If the block a Gear was on was destroyed, the Gear was not removed, but oddly, invisible. The Gear still existed in the map and would show up again if the block was replaced. Gears placed in mid-air using a map editor were also invisible and would show up if a block is placed next to them.

Gears were deemed removed from the game when their data value was taken and their sprites deleted from Minecraft's files. It is unknown what gears' real purpose was, but it can be presumed that they would've done things similar to what redstone can do. Before Indev was removed, it was still possible to hack in Gears and place them. It is now impossible to obtain or see first-hand gears anymore.