Fits to Singer and maybe others (outer diameter 20.5 mm, height 11.5 mm, bore 6 mm). 

As always I include the OpenSCAD source file for you to adapt and improve:

• 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 or even the OpenSCAD source code.
• 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