Check the listing for details. 36" Plenum Box for [36" Linear Slot Diffuser - (2 Slot) Double Slot] Premium Ins. Condition: New. Listed at 179.99 USD. Galvanized sheet metal Plenum Box with black foam insulation, ideal for Texas Buildmart 36" lineal slot diffuser. This air-distribution box attaches directly to the supply of the HVAC equipment that heats or cools the air. Connects to: 10" flexible duct in oval shape. Can be used and brazed to a 4" or 6" wood stud. If you do not have this size flex, you can use a reducer to modify the size. Professional HVAC Installer is Recommended.Ideal for Texas Buildmart 36" Lineal Slot Diffuser - 2 SlotGalvanized sheet metal Plenum Box with foam insulationTotal Box Dimensions: L: 36 7/8" W: 4 5/8" H: 11 7/8"Entry size: 10" flex in oval shape This air-distribution box attaches directly to the supply of the HVAC equipment that heats or cools the airIf you do not have this size flex, you can use a reducer to modify the size Here's a link to the diffuser that fits this Plenum Box:36" Linear Slot Diffuser - 2 Slot - AC Vent - Register