Apple Universal Dock Adapter 3-Pack for 20 GB and 30 GB iPod 4G, U2 iPod (White)  (Discontinued by Manufacturer) Compatibility: 20 GB and 30 GB iPod 4G; U2 iPod Enables any iPod model to connect to the iPod Universal Dock and other products that use the Universal Dock system Each package includes three Dock Adapters; choose the adapter that fits your iPod model When you want to connect a different-size iPod, simply pop out the Dock Adapter and insert a new one For use with 20GB and U2 Special Edition iPod with color display