They were 7/16 whitworth as whitworth measures the width of the thread, metric and A/F (Across flats) measures across the flats of the nut ie 21mm for your normal fitting. I don't think there's many 1/2" whitworth out there now.
---------- Post added at 08:17 PM ---------- Previous post was at 08:16 PM ----------
11.11mm is the same thread diameter as 7/16 whitworth