Connect motor shaft to anything else with a set-screw coupler. These couplers are made of machined aluminum and have a spiral cut that makes them slightly flexible so they can be fit to two shafts even if they are not perfectly co-linear and will help reduce bending effects. 

The way they are cut, create a spring effect in the X Y & Z linear axis but not in the rotational axis. That means that you will not get increased backlash - so they're suitable for precision CNC work.

This coupler will connect 4mm diameter shaft to  4mm diameter shaft. Comes with two sets of double set-screws (two per side) for secure attachment. You'll need a 2mm allen wrench to tighten/loosen the set-screws.

• 4mm inner diameter / 4mm inner diameter
• Outer diameter 19mm
• Height: 25mm