Review on EOWPOWER Pneumatic Straight Connector Fitting by George Saunier

These blue ones with DOXU printed on top of the plastic flange are the best and keep the pipe from moving when retracted. The only problem is that if your pipe tries to twist too much, it will spin and the metal teeth will start cutting into it. I ended up using a printed PC4-M10 fitting with a modified extruder frame to accept it. It works more like a compression fitting, preventing the tube from rotating and allowing it to go all the way through the extruder gear for a fully constricted filament path.