i3 X-carriage for LM8UU with 45mm rod center-to-center

This is an X-carriage, inspired by others like:
http://www.thingiverse.com/thing:889407
http://www.thingiverse.com/thing:1103976

These are both great carriages, but I wanted something I could modify easier, so this is made in FreeCad. Sources included.

Uses zipties to secure the linear bearings (LM8UU).
Belt is fastened with a "teardrop" loop.

Supports the 'standard' i3 rework 4mm mounting holes 23mm apart in a 2 by 2 configuration.
45mm 8mm rod center-to-center.

As of now, this