1.  Use a wooden or plastic tool to pry the upper sight strap out of the base past the "EARS" on the rear.  This will keep from scratching the bluing.

2.  Screw the wheel (counter clockwise) into the threaded hole in the top strap about ONE turn only.  Check and see that it can't wobble out and the screw threads are engaged enough to hold it.

3.  Screw the small inner bolt ALL the way into the wheels threads and then BACK it out about 1/2 of a turn....so that the little protruding bar will line up with the open slot in the base piece.

4.  Using the wooden or plastic tool, pry the top strap back into line with the base so it settles back in between the "EARS" of the base.  You will need to make sure the little protruding bar does not hit and get turned....so it will slip into the slot in the base.

5.  No you should be able to raise and lower the sight.  The wheel should tighten up on the inner screw in time to keep it from becoming unthreaded from the top strap of the sight.

Those Mossberg Boys were sure incredible at coming up with simple, but ingenious sights for their firearms!  Hope this helps.     ALAN

Special thanks to Ron Allen Clawson, may he rest in peace.

Alternative Method of Timing the S-102 Rear Sight

Screw the inner screw all the way into the outer adjusting screw.  Lift
the leaf with the nose of a Bic pen or equivalent about an 1/8 inch or
so, no need to shift it out of line.  Screw the adjusting screw
counterclockwise into the leaf about 1 full turn or until it is no
longer jiggly and feels like it will fall out. Then release the leaf
letting it fall to it's natural position, continue turning the adjusting
screw counterclockwise until the inner screw finds the notch, which
should be no more than half a turn. The sight is now set at it's lowest
point and can be adjusted up. This of course can be done w/o removing
the sight from the gun.

Special thanks to Jim Katz for shortcut!