For front sights screw size there's no one-size, they've used 3-48, 3-56, 4-48 and 6-48 for sure at one time or another, most I've seen are 3-48 tho. I made my own by cutting a 3-48 screw then cutting a slot in it with the dremel. I've also order some 6-48 socket heads from Brownells for the bigger ones.
Tim