12FT Stainless Steel Braided Propane Hose Extension Assembly with 3/8" Female x 3/8" Male Flare for Gas Grill, RV Fire Pit actual outsize overall dimensions is

actual outsize overall dimensions is 10“ wide by 8” high

The listed size 8" x 4" is for the inside duct opening measurement

PERFORMANCE SPECS- Outstanding range of chemical resistance

it refers to the size of the "tongue"  so that it will fit in a 8"x8" hole

12FT Stainless Steel Braided Propane Hose Extension Assembly with 3/8" Female x 3/8" Male Flare for Gas Grill, RV Fire Pit actual outsize overall dimensions is12FT Propane Extension Hose Assembly with 3 8" female x 3 8" male flare fittings. Key Features: 304 stainless steel braided hose assemble with inner tubing made of flame resistant material and solid brass fittings for safety and durability standard 3 8" female x 3 8" male flare fittings Compliant with ANSI Z21. 54 CSA 8. 4 Working pressure 0 350PSIG Outdoor use only