The ISO and Italian fork threads are the same diameter and pitch, except that 1" ISO (BSC) has standard 60° thread forms and the Italian 25.4mm is a Whitworth 55° profile.
They're close enough that folks have long since stopped worrying about the difference.
Usually, the underside of the locknut has the thread info stamped in, or if you have a magnifying glass, thread form gauge and good eyes you can read the fork.
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Last edited by FBinNY; 12-09-16 at 06:57 PM.