Wanted to try flex on my mini select. Found the original design by jspooner, but nut for push fittings is too thick. I reduced base size, and its fits better. Works great !!!

BTW - Jspooners directions are very clear, but Let me add. You need to remove the upright with some needle nose pliars. Clean out the hole in the base (push some filament through and adjust. The piece simply slides snug into the space. You will have slowly guide the flex through as it is flex ! I dialed back retraction and speed at first, but I noticed I could ramp up speed to 60mms withouth any issues. The key is dial back retraction. I just finished a 7 hour flex print, no issues.

EDIT: - You obviously can leave this in the extruder. I have been printing Petg on my mini all week with the space in. Looks like a permanent fix

EDIT 2: - Ran Pure TPU through also, and it prints like budder !!!!! I dialed back retraction to almost zero and print at 40mm/s. No issues.