I needed a 5mm to 5mm flexible coupler to mount a stepper motor that I salvaged from a 3D printer to a linear actuator. These are not expensive but I needed to have it ASAP. I did not find one that fit the bill so I designed one! 

The end pieces are printed in PLA-CF with 3 walls and 25% infill, and the middle in TPU with 2 walls and 15% to give a bit more flex. 

Tolerances are pretty decent and the pieces snap together. End pieces have a larger hole on one side to fit a small heat-set threaded insert. Will it last a lifetime? Nah probably not. But will it work for now? Hell yeah!