This thing is an experimental printable elastomeric coupling designed for a molded and cured-in-place rubber insert of RTV silicone sealer. This is a revision of http://www.thingiverse.com/thing:7687This version should be stiffer, and self centering.It has robust clamping, and should be well balanced if tightened evenly.HD Macro video of it being printed: http://www.youtube.com/watch?v=rkfMtFEaQG4Heritage -- this is a variation of these two couplers: http://www.thingiverse.com/thing:7678 http://www.thingiverse.com/thing:7687Print the parts. Use a solid profile for strength. Clean up. Run a 3mm drill through the clamping holes.The clamps will have good clamping force, but limited travel. The part should press onto the shafts with some reasonable force. If they are loose on the shafts, please make the shaft hole sizes slightly smaller and re-print.The idea is to fill the three spherical cups with RTV silicone sealer, and press the top piece in. Kind of jiggle it around to work the silicone in all the spaces. There are index notches that will engage to assure alignment. Make sure these are engaged so that the silicone has the same thickness throughout the spheres.Let it cure in a warm place (on a heat vent or a sunny window sill). It may take several says (weeks?) to cure fully. The gaps are small and deep. Silicone cures by exposure to air, and the exposed surface is small.Sublime points to a possible solution here: http://www.myheap.com/book/chapter-07/siliconecaulkmolds.php brendanjerwin reports good luck using hot glue.Clean off the excess silicone by rubbing, then carefully remove cut the alignment triangles. Once the triangles are removed, the coupler should have a slight flexibility in all directions, while still giving positive rotation and fair stiffness..Other materials could be used to get other stiffness. There are two-part silicones. Maybe Sho Goo ( http://bit.ly/hc11mc )?If you build this, please feed back what you use and how it works for you -- thanks!