Ok, so I think I have a handle on it now. Hope I do not sound like a dolt, but am I correct in assuming that the F-1 has smooth flat panels on the inside of the bed and is narrower than the F3 and thats why the fenders are a little fatter? I have compared pics of F1 beds and my F3 bed has a bump out in the inside of the bed at the bottom and I guess that is to accomodate the wider bed and to give the wheel some room?