Print without support. Make sure the first layer isn't too tight, making the knob fuse to the main pole. Thread the knob onto the pole before gluing the top piece on. Use 3-in-1 oil on both knobs to help them spin, and wear it in a little before sliding onto blinds. My blinds are just under 11mm in diameter and it is a wooden pole with a little warp that helps the fit a little. You can edit the Onshape document to adjust the inner hole size, but making it larger will require more edits.