I hope this is not a duplicate, searched product title but nothing came up...
Compatible with iPod with dock connector (10GB, 15GB, 20GB) 3rd generation.
Dock adapters enable any iPod model to connect to the iPod universal dock and other products that use the universal dock system.
Simply insert the dock adapter that fits your particular iPod model into the dock, then plug in your iPod.
When you want to connect a different-size iPod, simply pop out the dock adapter and insert a new one.