Were they on French bicycles with French hubs and early 1970s vintage? I have no doubt that Cyclo made freewheels with English/ISO threading, just as Regina made freewheels with French threading, however, it is my experience that French bicycles (Mercier,Peugeot,Gitane) made prior to the early 1970s used French threading thoughout their bikes. The only way the OP can tell will be to try an Engish freewheel, and if it is a sloppy fit, then the hub threads are most likely French. Since the difference in thread diameter is only 0.1mm and the thread pitch is nearly identical, it is near impossible to determine this by measurement.