Realized that I was using both a filament guide (http://www.thingiverse.com/thing:22649) and a spool holder (http://www.thingiverse.com/thing:20710/), but the filament guide was just wedged into place. By attaching the filament guide to the spool holder, it's held firmly into place.

And by fitting into the slider in the parent design, the filament holder can be adjusted to suit the particular filament and spool.

Print the plate. It's designed to hold the left spool. Mirror it before printing to make a holder for the right spool.

There are three pieces:

• The "Wall" piece, which attaches to the Replicator
• The "Spool" piece, which sticks out and holds the spool. It slides into the slot in the "Wall", nearer the outside edge of the printer.
• The "Guide" piece, which slides into the slot in the "Wall", nearer the center of the printer. The filament guide helps prevent jams by pulling filament towards the center of the spool.

Assemble the three pieces, then put the tab into the back of the printer and rotate the holder down so that the rod sticks straight out, just like the standard MBI spool holder.

Note that both pieces are designed to slide in the base plate so that they can be arranged as you prefer.

When you load filament, slide the spool onto the rod, Then feed the filament through the hold in the guide, then into the usual tube.