This is the small plastic winder that opens and closes the ventilation hatch in your caravan bathroom.

I found it too difficult to model the spline that it fits onto, so it's made slightly undersize and is therefore a rather tight fit.  The plastic forms into the spline to make a firm and secure fit as you can see in the photo.

It's designed using Tinkercad,  and printed on a Prusa Mk4.    Print standing upright, using PETG, with supports, 4 perimiters and 25% infil.