flat to 5mm shaft coupler

Use for coupling a 5mm shaft stepper motor to a flat surface like cardboard.
i used this to connect a cardboard VAWT to an old stepper so i could play with a multiple rectification circuit.

hot glue works well, easy to drill.
123d file attached for your use.

shaft has no flat as my stepper had no flat.
locking screw makes this compatible with round and flat shafts.
careful with the locking screw. too tight and you may split the shaft (thick collar and high infill and i have had no is