Elima-Draft 9 1/4" x 9 1/4" to 10 3/4" x 10 3/4" Insulated Magnetic HVAC Vent Cover For STEEL Vents Save up to 10% annually on your heating bills (Energy Star Home Rated) Keeps existing heat in where it belongs Eliminates cold drafts No tools required Fits STEEL vent size (outside dimensions): 9 1/4 x 9 1/4 up to 10 3/4" x 10 3/4" - WILL NOT WORK ON ALUMINUM VENTS. CHECK THAT YOU VENT IS STEEL BEFORE ORDERING!