An hairspring stud pin, as used on some cheap mov't is way smaller.
The advice given above is the right one, get a complete fork replacement. You are skipping steps for a beginner, get first to the point where you can comfortably service a reguar mov't without breaking or loosing anything, and enjoy the pleasure of having it run perfectly. You have plenty of time for more demanding repairs.
That's why a wrote "a bit". Anyway, a 1.0mm stem can have a 0.2 or 0.25 pitch, which means a crown tapped 3mm deep takes like 15 or 20 turns to full screw. One can have undercut 2mm and still have enough threads to hold safe.