Model originally uploaded to Thingiverse at https://www.thingiverse.com/thing:5271079.

These maths, phonics or anything to want them to be twisters are highly customisable. Choose which letters or numbers you want from OpenSCAD generate the STL files and print them. Three sides and up is supported though you'll need to play around with the height parameter to make sure there's enough space in the center for the locking tabs.

Use dual extrusion to print in two colours or print the rings, paint then sand the paint off the outer surface to create more contrast.

https://youtu.be/PFvm5V36KTg