Ipod nano to stereo attachment item?

I'll try to explain this as good as I can... There is an ipod attachment that plugs into the bottom of an ipod and it allows you to listen to your music on the radio (you have to turn it to a certain station) it doesn't have any wires, it just plugs into your ipod and it works. Could someone please find it on amazon or at least tell me the name of it so I can look for it online.