Step One: Turn your wingback chair upside down.
Step Two: Pull out any caps that are on the bottom of the legs (if there are any).
Step Three: Open the package of casters and pull out the threaded stems.
Step Four: Take the 3/8 drill bit and measure alongside the threaded stem.
Step Five: Take tape and wrap it around the 3/8 drill bit where you want the drill to stop when drilling into the legs.
Step Six: Take a pencil and mark an X on the bottom of the leg to find the center.
Step Seven: Drill a hole into the center, making sure only to go as deep as the tape allows.
Step Eight: Take the threaded stem and hammer it into the hole.
Step Nine: Place the caster into the stem and hammer it into the hole.
Step Ten: Give it a good tug to make sure it is securely placed inside.