A ratchet mechanism: the sawtooth gear rotates inside the outer wheel in only one direction due to the integrated spring-loaded pawl which blocks backward rotation but moves out of the way for forward rotation. Warning: This is an experimental, work in progress, proof of concept, and part of a larger unfinished project. If you just stumbled upon this, you may want to come back when the project is further along -- it's only here so people can play around with the mechanism. Reddit discussion about this item: http://www.reddit.com/r/3Dprinting/comments/2bp6np/functional_ratchet_mechanism_3d_printed_in_abs/The Outer_Wheel_with_Integrated_Pawl is not finalized and in need of a better support solution, so it needs some cleanup after printing because the roof falls in a little bit. (Adding generic support will likely destroy the spring mechanism by placing support on top of the spring.) It should be printed at 0.1mm layer height and scale should not be adjusted. It is scaled so that the spring mechanism is exactly 1-layer wide for maximum flexibility and in a continuous curve for minimum breakability.