Query: 8 x 4 linear ac vent
4" x 8" Return Air Grille - Sidewall and Ceiling - HVAC Vent Duct Cover Diffuser - [White] [Outer Dimensions: 5.75w X 9.75"h]
8"w x 4"h Adjustable AIR Supply Diffuser - HVAC Vent Cover Sidewall or Ceiling - Grille Register - High Airflow - White [Outer Dimensions: 9.75"w X 5.75"h]
8" x 4" Standard Linear Slot Diffuser - HVAC Vent Cover - AC Register - Single