If you do not mind a 10mm screw fitting, try https://grabcad.com/library/bowden-coupler-1by Dagnall53 - Object repositories
Hi, just signed up to the forum whilst looking for data on Traction Extruders. FYI, I have designed a version of a traction extruder that uses a 200T GT2 belt and geared wheel configuration. I have it on thingyverse: It has been running well for a few months now . (Note the "output" is "UP" in this image) It can print with a maximum filament force of about 2.5KGf (Say 25 Newtons) (measured witby Dagnall53 - General