I am absolutely in love with this game! The puzzles are fantastic, the graphics are great, the music is fun, and you have separate, easy to find mute buttons for music and sound effects. I think my only three real qualms with it at the moment are:

1. The star effect in the center of unplaced gears is kind of an eyesore and rather distracting

2. It can be a bit difficult to click on some of the gear edges, especially with a bunch of chains in the way. You might consider adding a bit larger a size difference between gear layers.

3. It'd be really nice if Newsground medals were enabled.

Otherwise, great job! I'll definitely be checking out the others in the series.