Surprising that it has not been posted before. I found the stock K8200 extruder quite unhandy when it comes to changing filament and I'd like to try TPE flex filament. I used http://www.thingiverse.com/thing:18379 and http://www.thingiverse.com/thing:498238 with a E3D v5 knock-off for 3mm filament. When printing 3mm TPE do not overtighten the filament bearing! This leads to compression of the elastic filament and it doesn't fit into the hole anymore which leads to bending and jamming. The hobbed bolt grips flex filament quite well so you don't need too much tension. The mount makes it easy to change extruders, since you only have 2 bolts holding them to the printer. Print with reasonable infill (70% +). Mounts with 2x M4x20 (extruder) and two 30mm long threaded rods and nuts to the printer Z.