Enif's design is really good, everything gets oriented so the end part is the strongest it can be.
I needed one for Z-leadscrews and cable ties. I also rotated the endstop so it can print without support (other parts may still require support depending on your printer).
Enif's original: http://www.thingiverse.com/thing:514582,
Also inspired by 3ed_de's addition of cable ties (zip ties) http://www.thingiverse.com/thing:894915
The OpenSCAD has the z-leadscrew and cable tie code are in the .scad file. It's called "ziptieCavities" in case you want to get rid of the cable tie holes.
For the Idler bearing holder or the endstop, it's easiest to get it from Enif's original: http://www.thingiverse.com/thing:514582
Thanks for Enif for this, I really learned a lot about OpenSCAD on this project.
see Enif's original: http://www.thingiverse.com/thing:514582
I'm currently printing my own verison of this in PETG and it seems to be much more dimensionally stable than the PLA I used earlier, the PLA shrank noticably ove the last few months.