Ok guys, lets hope this isn't a stupid question! What is the difference between the threading on an old 6 speed freewheel rear hub and a new threaded fixed/ss hub. Will a new ss or fixed cog thread on and work on those old hubs or what kind of modification has to be done in order for this to work. Will there be chainline issues...etc? It seems like more people would do it if it was easy, so I'm guessing there are big differences...help!