If you haven't ordered and received your Airtag Holder, you can ignore this. All new holders are shipped with those rubbers. These are only for the customers who already got their holders
My holder arrived without these inserts, so I ordered this pack as a spare—they fit perfectly and keep the AirTag from rattling around inside. Even after a month of daily use, they haven’t stretched out or slipped once. The material feels denser than I expected, which is a good thing.
The silicone fit is snug enough that my AirTag doesn't rattle around inside the holder anymore, which was my main gripe before. These inserts do exactly what they're supposed to, and they were easy to pop in.
Had to grab these because my original holder didn't come with the silicone inserts, and they slide in perfectly snug. The rubber adds just enough grip that my AirTag stays put in the holder now instead of rattling around. Exactly what I needed to finish the setup.