I have a PAL NES, but I think that US NES will be te same. At the bottom of the NES Box (and when I say box I mean the plastic that covers the chips, don't know how to call it because I'm not english/american). At the bottom of it there is something removable, don't know at all the use of removing it. I tried puting the RF Box there but doesn't fit properly at all. I tried it to try something, and because it's the only thing I thought could fit there. Anyone knows something about that? Only for curiosity.