Building a Kossel Mini? If you can't find those ball rails spec'ed for it, don't want to wait until the [Kossel Pro kickstarter](http://www.kickstarter.com/projects/ttstam/openbeam-kossel-pro-a-new-type-of-3d-printer) ends, and want to save over $50, this part gives you another option.
This is a Cerberus Pup-style carriage for Kossel Mini. It provides smooth motion with low cost (~$70 for 3) on OpenBeam, using [Graber Dual 623 V rollers](http://3d.grabercars.com/?product=dual-623-v-roller). It supports an unmodified Kossel ball joint adapter ([ball joint adapter](https://github.com/jcrocholl/kossel/blob/master/carriage.stl)) since the 20x20 m3 grid matches the spacing on the ball rails specified for the Kossel Mini. Just drop it in, and besides this part, nothing needs to change on your Kossel Mini build.
If the [ball rails sold by OpenBeamUSA](http://www.amazon.com/OpenBeam-Recirculating-Ball-Rail-400mm/dp/B00C440XCU/ref=sr_1_10?s=industrial&ie=UTF8&qid=1372289307&sr=1-10) are:
* not in stock,
* too expensive ($150), or
* not long enough (only 400mm limits Kossel size to slightly over 600mm)
... then this part may be for you.
Requires 3x [Graber Dual 623 V rollers](http://3d.grabercars.com/?product=dual-623-v-roller) per carriage, which are $7.45 apiece.