A box for storing sewing machine bobbins.  Fits either 16 or L bobbin sizes.

The fit between the lid and the slot is pretty tight.  If it doesn't slide reasonably easily, reduce the z axis scale of the lid a few percent.  Be careful to not pinch the sides of the holder while inserting the lid.

I was able to print the “Bobbin Holder” without supports, but the quality of the slot for the lid will depend on your printer's bridging characteristics.