This Door Mail Box Slot in Solid Brass, is designed for use in any Door, including Wood Doors, Steel Doors and Fiberglass Doors This item is only the Door Mail Box Slot. Overall Size- 3 3/4" High x 13 1/8 Wide Opening for Mail Box Slot is: 2 3/8" High x 11 1/8" Wide For Wood Doors you can use the Door Mail Box Slot, but the Door Sleeve is optional. Steel Doors and Fiberglass Doors would need the Door Sleeve, since you may want to cover the interior of the Door. Note: The Door Mail Box Sleeve must be purchased separately.