The Bowden clips on the Ultimaker 2 hold the Bowden clamp from retracting, and also keep it aligned square to the feeder and print head. You should not be able to see the Bowden tube and clamp move when filament retracts.Because holes where the Bowden clamp is inserted vary in size, the distance from the flange on the clamp and the feeder or print head differs between machines, so the clips need to be fitted to each UM2.These Bowden clips are supplied in 26 shim thicknesses from 1.0mm to 3.5mm, in .1mm increments. Use the thickest one that fits under each Bowden clamp at the print head and at the feeder. When you have a clip that fits properly, it should stop visible movement of the Bowden clamp and hold the Bowden tube perpendicular to the surface. These are derived from the Ultimaker 2 Bowden clips by 0perat0r  (Stephan Richter) at http://www.thingiverse.com/thing:300727