These rulers measure front-to-back edge-to-edge distances, i.e. the ruler takes account of the size of the base.
Choose the file 12inch_25+28+32mm_multipart_ruler-upload.3mf, which has 12 inch rulers for three base diameters.
I've prepared models for 25, 28 and 32mm bases in 4, 6 and 12 inch lengths. You can generate other sizes using the OpenSCAD code (or ask me in a comment).
One set of models is optionally multicoloured, and clips together after printing. The other is print-in-place, although it's a tricky print as the ruler is long as the contact area is small. Test with the 3 inch ruler first!
If the clip-together pegs are too tight or too loose, and you don't want to glue them, you can create other sizes directly in Prusa Slicer. Add a 4mm high × 3.8mm diameter cylinder, and then add to that a 0.6mm high × 7.8mm diameter cylinder. Adjust according to your printer.
The author marked this model as their own original creation.