Still in progress. This is a harmonic drive for a nema 17 stepper. You need a few parts to complete this.

4 M6 x 10 or 12mm long Button head cap screws. (wave generator) 4 x 606-2rs bearings (wave generator) 24 x M3 X 16mm Flat Head Cap Screws (at least 12) 4 x M3 X 5mm? Flat Head Cap Screws (for motor) Nema 17 Stepper

I printed all the parts with matterhackers pro ABS and the flex spline with Taulman Bridge. I use 1.2mm wall, and 1.2mm top and bottom, 15% infill, 1.009 scaling.