Locking Rigid Shaft Coupling

1.5 degree tapered threads on coupling and nuts enable the coupling to lock onto the shafts.

Stepper Shaft Diameter: 5 mm with flat
Shaft Diameter: 8 mm
Overall length: 25 mm

I have not installed this in an application, I just created it to see if I could get PLA to grab tight enough to a round shaft. It grips very well. The key component is the PTFE tape applied to the threads. This tape drastically reduces the friction between the nut and coupling threads.

8/17/13 UPDATE:
Per request, I have uploaded the source Autodesk Inventor files. These files are all contained in the file DoubleScrewCoupling.zip. There are five files related to the coupling and five related to the nut.

COUPLING: DoubleScrewCoupling_8x5.iam, DoubleScrewCoupling.ipt, DoubleScrews.iam, TaperedThreadShort.ipt, TaperedThread.ipt.
NUT: TaperedNut.iam, TaperNut.ipt, TaperNutScrew.iam, TaperNutBase.ipt, TaperedThread.ipt.

Increasing the thread clearance for the nut requires changing the FLUS