I use this set to create my motorized sky light shades. I have 4 pairs for each skylight window. The windows are angled so I use a rod on the top of the window to roll up the curtain/shade and a chain on either side to keep the shade at the same angle when rolled down. The bearing is 8mmID/22mmOD and fits very tightly into the wall mount. Spacing below the race ensures perfect free spin. The pulley fits a 4.5mm beaded chain. I derived it from http://www.thingiverse.com/thing:867 extending the points a bit to make it grip the chain perfectly. The curtain rod or roller is a lightweight 7.5mm aluminum rod with a star shape that locks into the pulley. I salvaged this rod, but I've seen them at HD and Lowes for cheap. Small sample of the rod is in the pics. Added a clip that slides on the rod, makes the curtain attach to the rod easier. I used 4 clips spread out on the rod. I printed this in PLA at .35mm layer height out of a .5mm nozzle. 15% infill.