17-1/2x23-1/2x1 (17-1/8x23-1/8) Accumulair Diamond Filter MERV 13 4-Pack MERV Rating: 13 Nominal Size: 17-1/2x23-1/2x1 Actual Size: 17-1/8x23-1/8x3/4 Part Number: FD17.5X23.5N Package Quantity: 4-Pack