HVAC Side Outlet Ceiling Box 6x6x4 (6"x6" Square to 4" Round) 30 Gauge with drywall flange - Connects to Air Register 6" x 6" x 4" Side Outlet Ceiling Register Box for home HVAC Duct Vent 30 Gauge Sheet Metal Duct Box Easy to install Retaining ridge around inlet neck to ensure snug fit to flexible duct Drywall flange for secure installation and serves as anchor point for register screws.