So, I went outside to finally remove the stock AM radio from my 1971 Chevelle and install the Audiovox AM/FM Stereo 8-Track unit I finished repairing (I have a quad one to eventually install when I do rear speakers). I found that the radio nut is not a standard radio nut of the kind I had a socket all prepared for. What type of nut is this and what sort of tool/socket do I need?