It seals off the open hole in the Door to Body Weatherstrip & gives the weatherstrip a more finished appearance.
These parts fit: 1983, 1984, 1985, 1986, 1987, 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, and 2004 Mustangs.