This is a flexible coupler for a delta printer I'm making. The flexible part is cast elastomer material using a 3d-printed mold.
The 12mm ballscrew side needs a M3x10mm bolt and a nut. The motor-side needs a M4x12mm bolt plus nut. Size selection was due to space and what I have on hand.
I cast the spacer in Smooth-On Dragon Skin 10 Fast however the end item is on the soft-end. I would suggest a Shore A 30 hardness to make the coupler a little more rigid.
Interference is expected, this is meant to be pre-loaded. This will put a bit of vertical load on the motor as well due to design. I'm using that to minimize movement elsewhere in the system.