This spool roller was inspired by (and fits onto) this nice spool holder by frank26080115https://www.youmagine.com/designs/ultimaker2-filament-spool-holder-by-frank26080115I wanted a ball bearing roller to fit this holder.  The bearings fit a bit tight, but I pulled them into the roller using the nuts.  You can adjust the model to fit other bearings if you need/want.If there are questions about what parameters to adjust, please ask, but it is intended to be self explanatory.Installation of bearings into the roller:1) Place 1 fender washer onto the 1/4" bolt and let it slide against the hex nut2) Place 1 bearing onto the 1/4" bolt and slide it against the fender washer.3) Place the spool roller onto the bolt4) Place the 2nd bearing onto the bolt5) Place the 2nd fender washer onto the bolt6) Screw one of the nyloc nuts onto the bolt7) CAREFULLY tighten the nyloc nut, while ensuring that the bearings are pressing into the roller correctly (the bolt should hold them straight - make sure they are centering in the roller and not caught on an edge)  As you tighten the nut they will be pulled into the roller.8) Remove the nyloc nut9) Remove all parts from the bolt - the bearings should not come out of the roller10) Place the bolt through the roller bearings and put one nyloc nut on.11) Place one fender washer on the end of the bolt12) Insert the bolt through Franks spool holder13) Place the 2nd fender washer on the bolt14) Place the 2nd nyloc nut on the bolt to secure the assembly into the spool holder15) Mount the spool holder with nifty roller onto your Ultimaker 2 and enjoyThanks for reading,  suggestions are welcome