Every car's cup holder and every tumbler brand's diameter is slightly different,
so generic "universal" adapters from Thingiverse either rattle around or don't
fit at all. CustomFit3D generates a parametric adapter sized exactly to YOUR
cup holder and tumbler — enter your measurements, preview the fit in 3D, print
a free 3mm fit test to confirm before committing, then get the full STL/3MF +
print guide for $4.99. You'll need your own 3D printer to print the files.
