The knob you use to open/close ceiling vents. Somehow my mother lost two of them, so I designed a replacement.

Two versions, one with a long handle like the original. The other one is shorter and works just fine and prints a little quicker.

I suggest printing it on it's side as is with supports tuned on for strength. Also use a high infill if your vent is a little tough to open like mine was. They're old and might be a little rusted so they stick and a few prints I did got twisted/broken with low infill.

I made it with OnShape, you should be able to copy/edit it here I think.