Atlas Sound 81-4 4" Round Hole T-Bar Bridge features a round cut-out and is fitted for 4" loudspeaker baffle Models 51-4 and 60-4. It is very genius by having a Load-Bearing Bridges to avoid Ceiling Tile Sag because it distributes an even weight to the ceiling's support system. Its Rust-Resistant 24-Gauge electrogalvanized Steel Construction guarantees a lifetime service.