Grommets for Tzitzis

Why aren’t grommets use for tzitzis?

Answer:

There is no special halachic reason why grommets aren’t used for tzitzis, and it is permitted to use them.

Although the actual garment must be made of wool (on a Torah level) or another garment-like material (such as cotton, which is obligated on a rabbinic level), the metal of the grommet will not alter the essential nature of the garment, and its status in halachah will not change.

In practice, it is rare that tzitzis strings tear through their holes, and it stands to reason that grommets are simply unnecessary, which is why we don’t find them commonly (or at all) used.