Most of the 6 inch or 8 inch round speakers I install have built in "dog ear" brackets. You must remove the grill to acccess the screw heads. The dog ears look like 4 plastic tabs near the outside perimeter of the speaker. each ear should be sitting on top of a slotted post with a screw inside the middle of each post, which penetrates through the "dog ear". Most of the time the box that the speakers are packed in have a cardboard template in the packing. The template is a bit smaller than the diameter of the speaker, and the ouside edge of the speaker becomes the trim to cover the edges of the hole. When the speaker is inserted into the hole and the bracket screws tightened, it spins the dog ear brackets out over the drywall. The tension from the screw on the dog ear againt the top of the drywall holds the speaker tightly in place.
