Drop ceiling speaker brackets for in-ceiling installation in commercial facilities with paneled ceilings.. For use with product ID 4104 (mst-870-2y). this product is not compatible with product ID 4929 (mst-825a). This installation kit is designed to mount a pair of circular 8 inches in-ceiling speakers to the acoustic tile of a standard dropped ceiling with 24 inches x 24 inches or 24 inches x 48 inches panels. It has a 9.5 inches inside ring diameter, which allows it to mount speakers with a 9 ~ 10 inches cutout. It includes a bridge bracket, which spans the width of the ceiling tile and puts the weight of the speaker on the ceiling frame instead of the tile itself.