For a horizontal through-the-wall installation here is the thimble to use. It is used to maintain your 1in clearance. This wall thimble is designed to fit between standard wall studs and accommodates a maximum wall thickness of 7in. You will need a 7.5in X 7.5in square hole.The black portion of the thimble attaches to the interior wall to give a nice finished look and the galvanized section attaches to the exterior wall. You will want to use a House Shield to finish the exterior when vinyl siding is present.