3D Printer 4xLM8UU Minimal X Carriage (with symmetric/balanced tensioning mechanism) for F694zz bearings & more [#SCOUTcorexy design]

This is the evolution of the 3xLM8UU Minimal X-Carriage with balanced belt-tensioner (http://www.thingiverse.com/thing:1505842) that I have previously developed for SCOUTcorexy 3D Printed (http://www.thingiverse.com/thing:1487375).

It is not replacing it as that one servers the purpose very well but this is an effort to have 4 bearings for those who want them.

I made this one modular so I or anybody else can just replace the belt-grippers at will, printing them alone if the bearings on their Y axis changes for some reason without re-printing the whole X carriage. I have added a way to fix one module to the X Carriage body should you decide to go for the modular approach (expecting to change them at some point and don't want to re-print the carriage), namely a nut in the body of the X-carriage which will restrain the movement of the module opposed to it.

The advantage of increased rigidity due to the internal belt grippers is maintained.

Please ask questions if you have any, I will try to respond to every single one of them.
You might also be interested in the 3D printer I am designing this X Carriage for: http://www.thingiverse.com/thing:1487375 (View it in 3D @Sketchfab: http://is.gd/1l27lz)

Update 08/07/2016: added the YCarriage that goes with this XCarriage design. Distance between rods 40mm.