which is about 3/4" or so wide. If you're holding the shim, the end with the small indented circle should face away from you and slide in first. The end with the the two flanges and the elongated oval indententation faces out and the raised part should look like a little ramp leading into the dock. It might take a little trial and error, but ideally you'll find one that is just tall enough so that the back of the ipod sits on it when it's level in the dock.