Attached is a openscad and STL file for a carriage that used screws as rebar for added stability, and fixes the belt by looping it back on itself. It also allows for a lot of freedom in movement for the push rods, and mounts to the standard linear rails easily. I created this to replace the makergeeks carriages I had received with my kit, which did not hold up to the pressure of the belt. Many thanks for all the ideas people shared in the rep-rap forums and here on thingiverse. More information here: http://sebastian.steinhauer.info/index.php/2015/09/09/mini-kossel-building-a-better-carriage/ You might need to print with support to avoid sagging of the push-rod mounts. But be sure to keep the alignment screw channel free of support. I have the part printed in 0.2mm PLA, with 70% infill in operation for 2 months now, and I have not seen the belt slip or the part deform.