HVAC Plenum Ceiling Box 12 x 12 x 10 (12"x12" Square to 10" Round) 30 Gauge with drywall flange - Connects to Vent Register Diffuser 12" x 12" x 10" 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.