I won't actually be helpful here since I don't know the correct size, but am pretty sure it's size human hair. And if I remember right, the hex wrench that comes with either the Crimson Trace Rail Master or the Laser Max UNI works. I have a pill bottle full of the laser and PVS-sized hex wrenches and one of the lasers uses a bigger one and the other laser and PVS wrenches are interchangeable. So, if you've got one or both of the lasers, you might get lucky.
What I do is adjust the eyepiece first, by turning it to focus on any small specs on the screen. This will get you close, you will see the extremely fine grains as you focus the eyepiece. Then look at something in the distance and focus the objective/front lens turning it cw or ccw till the distant object is very clear. Then I look slightly above the horizon and keep my head still and only look down toward the ground and fine adjust the lens. This works for me to be able to see close in and at a distance. I try to get the sweet spot for driving and walking around. Once you get it working properly you will be blown away!