After rearranging my Rigidbots on my wire rack, I needed a side spool rig to lower the vertical profile. The side spool holder fits on the left top rear corner of a Rigidbot (either original or RB2 or Big), and the guide fits on the left top crossbar. A push fit pneumatic connector screws into the guide arm, 5mm thread. A 2mm ID/4mm OD teflon guide tube guides the filament to the RB hot end (I drilled a hole in the spring arm and threaded another fitting into that hole). A 6" piece of 3/4" PVC goes into the end of the spool holder. In my case, I had to sand down the PVC a bit and it is a friction fit, but it could be glued in as well if desired. The tension nut goes on the end and holds the spool in place. Works like a charm and the feed is so smooth that I haven't yet had any coils fall off the spool and jam. I'm using this on both my RB2 and RB Big. This rig allows you to stack same size Rigidbots as well (with a spacer). I used M3-12mm screws to assemble, but any length longer than 10mm will do. The holes are sized so you can screw them in directly but if you want to use longer screws with nuts, you'll need to drill them out and use M3-30mm screws. I used 4mm pneumatic fittings with 5mm threads (specifically http://www.amazon.com/uxcell®-Thread-Pneumatic-Connector-Fittings/dp/B009ITFXDI) The limit switch arm uses the Sparkfun microswitch: (https://www.sparkfun.com/products/13119https://www.sparkfun.com/products/13119) The limit switch and code has not been tested yet but the guide arm can be used without it. If your printer board and software support it, you can wire the switch in and have the printer pause when the end of the filament is detected. That is DIY, however.