I designed this coupling to be printed in one print with 2 extruders - ABS & SemiFlex
You can also try printing it seperately. It's up to you. You will reqire M3 threaded inserts for this to work.
UPDATE: I added a 5 to 5mm version. If you require any other size please contact me or leave a comment. I also added a hole on each side for an additional M3 threaded insert for a grub screw.
If using slic3r, use the 'external perimeters first' for the Flex part.