Helical Cut Flex Coupling

25mm Long 20mm Diameter. Now 5mm AND 0.25" (6.35mm) Bore files. I designed this for a light duty Z-Axis Nema 11 stepper (28BYG501) for a CNC engraver I am building.

I rounded all sharp edges for a professional appearance and to eliminate stress risers that could lead to cracks. Let me know if I missed any edges.

UPDATE - 3/3/2012: I added 3 new versions with a 1.5 turn helix cut. Mouse over file name and look for ones with 1pt5 at the end. Hopefully more robust. The originals were modeled after an aluminum one I had and I didn't account for the obvious material differences.