Apple Universal Dock Adapter 3-Pack for 40 GB iPod 4G (White)  (Discontinued by Manufacturer) Compatibility: 40 GB iPod 4G 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 the 40GB iPod with click wheel