The belt is flexible and small to fit into medium to large holes. Also conforms well to both external and internal fillets

I suggest using 200-600 grit, and printing with PETG.

Model is slicer scalable, although provided scale gives the best results. Scaling will impact fillets which may not look as good.

WARNING:
Make sure your sandpaper is strong and does not rip with a reasonable amount of tension. Folding the paper over itself helps a lot with strength, although cut-up belt sander belts work best. 10mm*150-180mm.

If your belt ends up being top thick, scale down the front and back holder pieces in the slicer. Turn off uniform scale. Scale down by an extra 0.1mm-0.2mm in X and Y but not Z (vertical axis).