Optimus 4-Inch Flush-Mount Speaker System Preparation And Installation Manual page 3

7. Remove the grille from each speaker's mounting bracket to expose the
mounting holes.
8. Place the mounting bracket on the speaker.
9. Align each speaker's mounting holes and the mounting bracket's holes
with the holes on the speed clips, thread a supplied screw through each
mounting hole, and tighten all screws until they are secure.
10. Firmly press the grille onto each speaker's mounting bracket.
NOTE: You can use the supplied adhesive glue to further secure the
grille to the mounting bracket.
Press the glue into the mounting bracket's edges.