Inspired by Chris535's brilliant idea at https://www.thingiverse.com/thing:5316421. I use it for detergent and oil bottles.

Redesigned from scratch in OpenSCAD. My derivative does not need print supports. The openings may lead to stringing, so I added a "closed" version preventing this problem. As always I include the OpenSCAD source file for you to adapt or improve.

The .stl files are assuming a bottle cap outer diameter of 31 mm (plus a 1 mm air gap). If this does not fit your bottle: Do not give in, remedy is just 10 mintes away!

• Download and install OpenSCAD from https://www.openscad.org
• Launch OpenSCAD and open the enclosed OpenSCAD source file (/File/Open).
• Amend the parameters at the top of the file (see last picture above).
• Save your changes (/File/Save).
• Render the design (/Design/Render).
• Export the rendered design e.g. as a .stl file (/File/Export/Export as STL).
• Slice and print.

See my other designs at
https://www.thingiverse.com/thinger13/designs