This gadget clips onto the Bowden cable retainer on the top of the Ultimaker extruder. It makes retractions work considerably better (discussed here: http://groups.google.com/group/ultimaker/browse_thread/thread/7537389e8085beaf#)This is a different take on the remarkably effective and simple Quick Connect Shim (http://www.thingiverse.com/thing:22851). I found my shim would fall out from time to time, so I made this one which has multiple thicknesses, and (I think) clips on slightly better. It's also easier to remove, and slightly harder to lose ;-)This takes about 2 minutes to print, and doesn't need any special settings.