Retraction is used when the printhead needs to be repositioned without applying plastic. The hot, liquid plastic tends to oze out. To reduce this, the filament is pulled back a little before moving the printhead and the pressure of the filament is reduced to the nozzle. At the upper end of the coupler is a movable metal part. To release the hose, it is pressed down while pulling on the hose at the same time. The couplers come from the compressed air technology and were not developed for use in the 3D printer. The filament generates a friction in the hose. As long as the filament moves in one direction, there are no problems. With the retract, however, it is quickly pulled back and transported forward again. This can lead to a clicking sound caused by the movable coupler top. To prevent this noise, there is a simple solution. Mounting a cable tie, so that the coupler top stops moving, avoids the clicking sound.