36x6 Modern AC Vent Cover - Decorative White Air Vent - Standard Linear Slot Diffuser - Register Grille for Ceiling, Walls & Floors - Texas Buildmart

neck: 35 1/2" x 5 15/16" - face: 37 3/8" x 7 7/8" (The neck is the section that goes into the vent hole while the face is what will actually cover)