When I printed the MK4 extruder (http://www.thingiverse.com/thing:47561) replacement for Solidoodles Jigsaw I had to file down the peek holder to get it to sit far enough back that the filamnt wouldnt bend and break when trying to be fed down. The problem was this created a bit of a loose fit. the peek would actually hop up and down while printing. so this is a clip to hold the peek in place.