The grommet center hole and the hook is about 4mm wide. The inexpensive curtain is 0.1mm thick and this is made to fit its 6mm holes(~0.3mm thickness). If your curtain has larger holes or your hooks are larger or you do not want to mess with drill bit to clean up the center holes, you should be able to enlarge both X/Y axes from the slicer to make it fit yours. If your curtain is thicker, enlarge Z axis(bottom only) should work.
Was printed in ABS, not sure if PLA is flexible with short snapping tabs. Recommend to print 2+ sets, so that it has time to cool off between the layers and test fit before print more.
The center hole for my final print is a bit smaller than the hook 4mm size, so I use a drill bit to make the hole larger/cleaner. Alternatively I think enlarge the X&Y axes 10~15% should also work, but probably stretch the curtain hole a little bit during the installation. Match the slots on the cap(top) to the triangle on the base(bottom) before pressing them together.