I used super 12 bearings on my wood router. I noticed with a slightly loose fit, you can adjust the tightness of the bearings on the shafts by shimming the bearing in the hole with a piece of paper, or wrapping it with tape.

But, during assembly, I found that shimming them tighter wasn't necessary, due to slight misalignment of my whole assembly. The slight play made it self aligning, with what appears to be no play at all.