Sheldon Brown says: Italian freewheel and headset threads are the same as British/ISO, except for the thread angle difference. They may be interchanged, but you should not go back-and-forth bewteen Italian and British/ISO headsets. Italian freewheels are basically extinct, so the issue is moot there. Italian size handlebars/stems generally use a clamping diameter of 26 mm. Many high-end aftermarket drop handlebars and "road" stems also use this size even if not Italian made.