BIQ Stepper Motor D-Cutter tool kit provides a jig to hold and reshape a rounded stepper motor shaft to a D-shape.

The Kit contains:

1 x 6mm MDF motor mount.
3 x 6mm MDF D Shaft cutting guides.
1 x 6mm MDF Dust gard
4 x 3mm 20mm long Screws
4 x 3mm nylock nuts
4 x 3mm 10mm long Screws

Usage Instructions:

Fit a stepper motor into the round dust guard to the shaft.

Important: You must short connect all of the Stepper motor wires together to prevent the motor from turning while using the jig. I use a Chocolate block/Screw terminal block.

Then mount the jig in a vice to file, dremel or grind the D-shape on the shaft

This is as seen on Thingiverse here.