The drive wheel for the Van der Graaf-generator in my physics laboratory was broken. I was unable to find spare part and I was not able to find a suitable part here. Most pulleys are for drive-belts, not o-ring type rubber bands (round) that this apparatus has.
Uploaded a photo of broken part to chatGPT (o1) and it created the part for me in SCAD-code. After som tinkering and adjustments I got it right.

All parameters are simple to change in the SCAD-code with no prior knowledge.
With my printer I found that 6.5 mm axel hole was a good fit, even though the axel is 6mm in diameter.

To view and adjust the part I used OpedSCAD. Simple and intuitive (press F6 for rendering, F7 for exporting as STL or F8 for printing)

Adjustable parameters with default values

// Main adjustable parameters:
outerRadius = 10; // Radius at the largest outer edge (10 => Ø20 mm)
totalHeight = 20; // The overall "tallness" of the roller
axleDiameter = 6; // Hole diameter for the axle
grooveWidth = 6; // How wide (along the roller's axis) the O-ring groove is
grooveDepth = 3; // How deep (radially) to cut into the spool for the groove
heightFlatSection = 0; // How wide a “flat” region appears in the bottom of the groove (If set to 0 the part will have a simple V-groove)