Basement window inserts come in standard and custom sizes* There are 3 basic brands: Columbia, Kewanee, Monarch (look the same,but Different )* Inserts are available in sIngle pane or dual pane insulated glass* Steel buck frames have different outside drop downs for insertThe following Information is to help get the right product the first time:Drop Down Depth on the steel buck frame: Primary ImageKewanee drop down 5/8 to 1 inchColumbia drop down 1/8 to 3/8 inch Monarch drop down 3/8 to 5/8 inch The drop down is measured from the outside, from top ridge on the bottom section of the steel buck frame. See 2nd & 3rd ImageNormal spacing between metal clips: See 4th Image Kewanee 19 inchesColumbia 19 inches Monarch 15-1/2 inchesNOTE 1: Monarch will fit all steel buck frame. However, you will see the black weatherstip when used with a Columbia insert. The visual weatherstrip can be removedNOTE 2: If not sure what you need, contact office.