Took zheng3's bearing, pulled it into Rhino, and changed a few things to better fit my filament spool.
-Made the main diameter 30mm to fit my spool
-Added a flange to the outside of half so it'd stay put
-Made the inner diameter fit an M8 rod perfectly
The bearing is still split in half for easy BB insertion.
Printed on a Prusa i3
.25 layer height
A bit of infill
Any of these setting can be changed, this was just my setup
Once the pieces are printed, add some BB's, glue the two halves together, and you've got yourself a printed bearing!!!