UPDATE 20.JAN.2014: Added a new version (MicroWave V2) which is even smaller and has some more clearance towards the block, but should work just as good. Also added STEP files for both. Enjoy. :)Inspired by GIjs's Ultimaker belt tensioners (http://www.youmagine.com/designs/belt-tensioner). My belts are very old and slack so I needed additional tension. To achieve that I made these tiny tensioners, so I could fit 2 per belt. They are very rigid, especially considering their size, and should work with the standard UM bearing blocks without a problem. (I would love if someone could check that, because I don't have the stock blocks on my UM!)Print with 100% infill. Print as many as you need and slip them on your belts. Note that the belly of the wave should point away from the bearing blocks for clearance.