This same question was posted on another forum.
So, in the public interest, here's how to change out a S&W rear sight blade:
Removing the rear sight blade requires breaking the windage screw.
This is how the sight was designed by the factory.
Before doing this, you should buy the correct rear sight replacement kit.
This kit includes the correct height sight blade for your particular model, a new windage screw, and the tiny windage screw nut.
To remove the blade:
Using a PROPERLY FITTED screwdriver (NOT a S&W sight screwdriver) turn the windage screw COUNTERCLOCKWISE until it stops.
Then forcibly turn the windage screw until the screw shears in two.
(The windage screw has a weakened area in the center that's designed to shear under stress).
Gently bump the sight body on the bench until the windage screw moves out of the sight body.
BE CAREFUL not to lose the tiny windage screw spring and plunger under the head.
Push out and unscrew the other end of the windage screw and nut from the sight blade, then remove the blade.
ALTERNATIVE METHOD:
If the screw won't shear, or the screw slot is damaged, carefully use a drill to drill away the riveted end of the windage screw that secures the tiny nut.
To replace the assembly:
Clean everything up and remove all old lube, especially inside the body.
Re-lube everything.
Thread the new windage screw fully into the new blade.
Insert the windage screw spring and plunger into the their hole in the body.
Depress the plunger slightly and insert the blade and windage screw into the sight body.
Using a S&W windage nut spanner, or a small pair of tweezers, screw the new windage nut onto the windage screw until it just makes contact with the sight body, then BACK IT OFF 1/4 turn.
Rest the windage screw head on a brass anvil, and use a rounded-off center punch to carefully rivet the end of the screw over the nut.
This doesn't take much to lock the nut on the shaft, so don't over do it. All that's needed is to flair the end enough to prevent the nut from coming off.
Check the sight for proper operation by running the blade all the way over to the right and all the way over to the left to check for binding or restricted movement.
