Hub threads are one of 3 common pitches. 1mm, 24tpi and 26tpi. There are probably some others, but these are the most common.
Odds are your axle is 24tpi, though vintage European could easily be 26tpi.
Get a ruler and count the threads of the original axle, over 1/2" and you'll know. Or simply compar to see if the pitch is slightly closer or wider than the 1mm on the new axle.
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