I highly recommend using the further improved design at http://www.thingiverse.com/thing:18657, that jonaskuehling uploaded recently Prusa Mendel x carriage using 4 lm8uu linear bearings in screw-fastened holders for easy (dis-)assembly. No zipties, no fragile and imprecise snap-in-brackets.I didn't like the snap-fit bearing holders in Greg Frosts's x carriage for the same reason why jonaskuehling made the slim LM8UU holder derivate. So I modified Greg's carriage and integrated the new bearing holders for an easy-to-disassemble x carriage.I attached the OpenSCAD files including Greg's configuration for some variables and Jonas' lm8uu-holder. I tidied up the source code a bit, but there are still some unnecessary lines left over from greg's code. The code is not overly clean and parametric due to the lack of time.UPDATE 31.01.2012UPDATE 03.02.2012Print. Slide in 4 LM8UU linear bearings. Gently secure the bearings with 4 M3x20 screws and 4 M3 nuts.