I maintain that knowing the thread pitch (which, by the way, you could determine using a 5 or 10 dollar pitch gauge) is unnecessary. You shoot, asjust, shoot, etc., until it's hitting where you want. You'll be doing that to some extent, whether you know the thread pitch or not, anyway.
The other method, if you're looking for clues as to HOW FAR to move the rear sight, would be to measure the first group's Point Of Aim verses Point of Impact offset. Take the known distance to the target in sight radii (sight radius is the distance between the front and rear sights), and divide the POA/POI offset by the distance in sight radii. That's how far your rear sight needs to move.
Fire a group on paper at a measured distance (usually 25 yards). Three to five shots is usually enough, depending on your shooting skill. For an initial group I often fire only one shot, if it felt like a good shot. Maybe two. That will depend on your shooting confidence. - like I said earlier; you'll want to know your accuracy is good (meaning you're getting small groups, even if they're way off of point of aim) before you do any of this. Three to four inch, five-shot groups should be fairly easy to obtain with a basic Italian repro.
Let's say the center of your fired group on paper is twelve inches too high at 25 yards.
Say your sight radius is ten inches. (I don't know your sight radius - this is just an example - you'll have to measure it yourself)
Now convert the distance to the target from yards into sight radii;
First convert yards to inches-- 25 yards x 3 x 12 = 900 inches.
Now convert to sight radii; 900 inches = 90 sight radii (900/10).
Your group offset (12 inches) divided by 90 = 0.13"
Lower your rear sight by 0.13" (regardless of the adjustment screw pitch). Shoot another group to verify. Make further, finer adjustments as necessary.
You'll soon find that knowing the exact numbers becomes less and less necassary, because you can see very well whether your shots are hitting where you aim.
I'll only do that math when I have to file down a sight, or make a new, taller sight, so I have some idea of how much metal to add or subtract from the original sight. Otherwise it's "Shoot, adjust, shoot, adjust...", until the gun is hitting where you want.
The only time you REALLY need to know exact adjustment increment values is in long distance rifle shooting, where you're making sight adjustments for widely different distances on a regular basis, out past 300 yards or more. Pistols aren't generally used that way-- Typically you'll set the sights and leave them set, until you change loads or something and have to tweak the sights a tiny bit.
Get ye out into the field and do some shooting, and this stuff will all become second nature very quickly. Then you won't have to become bored by reading all our instructions.