I may have mistyped, but I was not trying to say that one could use a french threaded freewheel on a BSC threaded hub, rather the opposite. The PX-10 in my recollection came with French-threaded Normandy Luxe rear hubs and a freewheel with a matching French thread. If the chain or freewheel are worn on this bike, the freewheel will probably have to be replaced. That would require the OP to search for a French-threaded freewheel, or for a suitable substitute wheel with BSC threading.