Edit: I have now added a GT2 belt clamp so the motors can be in the middle as well! I also added some simple boolean variables in the .scad file to enable/disable what to use. What I find work here is to put in both ends into the clamp, and then tighten it with a m3 screw. Seems to hold it quite well! Then, to tighten the belt, you just move the top up. This is the paramereized version of the Cerberus pup vertical carriage you can find here: http://www.youtube.com/watch?v=Ypm4oHYM4Uo and here: http://www.youtube.com/watch?v=_Mn4U0srZGg I got the original from Steve (thanks Steve!), but wanted to add belt support as well. So I figured I do it with OpenSCAD. There really shouldn't be much to change, as it should be pretty tweaked and ready to use as is. Still, I like having it in .scad format. Works superb on Openbeam! The Dual 623 V Roller from http://3d.grabercars.com/?product=11-delrin-roller-with-608-bearing-fits-1515-series-extrusion-from-8020-net-copy really makes this excellent! I also love the tightener design. Furthermore, I added support for belts, using a clamp. Since I have a few of those Openbeam brackets, I also needed to put that belt on the side, which is why I also have that "belt holder" which can be screwed on the side and can be seen in the images attatched here. So, with this, it's up to you to use fishing line, or a belt. And, the belt can be either in the middle or on the side using the belt holder. Well, print it. Then you need a bunch of M3 screws. And, you need 3 Dual 623 V Rollers per carriage, ending up in 9 in total for all three. I also have a nut between the plastic and the dual 623 V roller to add some necessarily spacing.