Disconnect the power supply to the ceiling fan. Remove the fan blades. Remove the wire nuts and disconnect the wires. Remove the mounting and the fixture. Set everything aside.
Measure the width between the two ceiling joists located above the ceiling fan. Place the ceiling fan box between the joists, making sure it is a snug fit.
Slip the ceiling brace through the existing hole cut in the ceiling for the fixture. Position the brace to fit snugly between the inside edges of the ceiling fan box. Rotate the shaft of the brace with an adjustable wrench until the teeth no longer move in the joist.
Attach the bolt assembly to the brace, making sure the bolts point downward through the hole.
Cut one of the stamped holes out of the electrical box. Feed the wires from the ceiling hole through the cut-out hole in the electrical box.
Align the electrical box with the bolts that are facing downward. Push the electrical box over the bolts. Place nuts over the bolts. Screw the nuts onto the bolt assembly. Tighten with an adjustable wrench.
Attach the new mounting assembly to the electrical box of your ceiling fan box with the flat-side up. Secure the screws with a screwdriver.