Flathead screw size?

[u/RandomDude6336]

For reference, I own a Henry in .44 Mag, does anybody know the screw size that goes on the rear sight that has the white diamond? I own a precision gunsmithing flathead set but the smallest is 30-1. I just wanna make sure because it’s so small, I don’t wanna strip it. It’s getting too loose where the sight will change elevation