On my No. 4 it is held on by a screw, you unloosen the screw and then you can drift the site left or right. The screw itself is the negative of a normal screw so instead of a slot cut into the screw like a normal standard " slot blade" it is the reverse so all you have is the blade sticking out. All I did was take a cheap broken ended screw driver and cut the end off and with my dremel tool cut a slot down the middle of it that is the correct size for the sight screw, easy as pie.