Video here: http://youtu.be/bSbYbVXHCSA
Neat little two piece pulley and block so fit on top of an 8mm or 5/16" threaded rod, or screw it to the underside of a shelf above your printer.
The two pulley halves just fit together without the need for glue.
this is the best filament feed system I have come up with, it is very fast to change and lets you run multiple spools on a rack beside your printer http://www.thingiverse.com/thing:28944 or between them like I have done here.
Mine clips into the top rails of my Mendel Prusa via the mounting clamp I have used on other similar projects.
Print out the four parts, you need:
2 x pulley1.stl
1 x block1.stl
1 x mount1.stl
The last one is for mounting on the top two rails of a Mendel Prusa or similar so you can ignore this part if you are using a different printer or mounting the pulley to the underside of a shelf above etc.
You also need an 8mm bolt and nylock nut (or 5/16") and a short length (150mm - 200mm) of threaded rod with 4 nuts and 4 washers.
Print out all the parts, hot rod red is best for high speed applications.
Clean up the parts with a razor blade or scalpel.
Clean out the 8mm holes with a drill bit (run your drill in reverse to avoid grabbing and breaking small parts).
Snap the two pulley halves together then fit them to the pulley block.
Insert the 40mm long bolt through the block and pulley and tighten it up enough to engage the nylock on the nut but still allowing the pulley to move freely.
Attach the lot to the threaded rod and tighten nuts each end as per the photos.
Snap the whole assembly into the top rails of your prusa and that's it :)