I have been trying to get more reliable prints. One of the reasons my prints failed was because of the PTFE coupler moving during retractions, allowing small material to get in between the hot-end and the coupler. The spring is not needed anymore after the announcement that Dual Extrusion was killed off for the Ultimaker 2.This little tube will fit exactly over the PTFE coupler and inside the print head. if you keep 1 MM of space it will also fit nice and tight. when assembling, make sure everything is straight. apply final pressure (but not too much! with the 4 corner screws from the top of the hot-end. I have had a great improvement in retraction performance and reliability. Looking forward to comments.PRINTING INSTRUCTIONSi printed this with Colorfabb XT at 30 mm/sec with fans at 100 percent, 242 degrees. printing too hot, without fans or different material might cause this not to fit. experiment untill it fits perfectly.