Spool Bearings (double bearing with retainer)

Brief: This is a double bearing design with integrated retainer.

I had a few difficulties with my Rostock where it came to dealing with spools:

1) Spools did not want to turn freely on the spool holder.
2) The screw on the arm side of the holder would catch on spools.
3) The spool would jump over the lip of the stock holder.
4) All the above caused a variety of issues with printing.

My solution was to create a couple of spool bearings (with large side walls) which addresses all the a