Pillow block for 608 type skate bearing, slightly modified from http://www.thingiverse.com/thing:217391 changing mounting hole spacing, and overall thickness. 7 mm thick bearing sits on 2 mm lip and other face is flush with block surface. These dimensions give me a slip-fit on the 22.0 mm OD of the bearing in the block.
Photo also shows http://www.thingiverse.com/thing:399725 shaft adapter for fitting 6 mm threaded rod to 8 mm ID on bearing.
NOTE: Do not assume some cheap 6 mm threaded rod is anything like straight, at least mine wasn't. You don't notice a slight bend by eye, but when rotating on nominally fixed bearings, a bent shaft causes wobbles.