. Fitting. Position centrally over letterbox hole on door. Mark fixing holes on door with pencil. Drill pilot holes to receive screws and prevent screw damage. Fix into place with screws provided. Internal Or External Option. This Letter Box Cover can be used on inside or outside of door. It is completely rust free, rain resistant (stops rain entering / underside drain points for driving rain), will not blow open (opens outwards and spring-loaded to stay closed), designed with postman in mind (will open to almost 180 degrees), and twin brushes are removable before or after fitting if required. Sizing. There are different sizes of letterboxes and letterbox slot or hole cut in in door. Please remove your existing letterbox draught excluder (if one is fitted), measure aperture and compare dimensions (see image) before ordering.Box ContainsLetter box cover; fixings