This is the rubber that goes into the bracket of the bottom of the center of the door, for 1969-1970 Mercury Cougar and Ford Mustang glued-in door glass.
Note that this bumper is substantially shorter than the 70 bolt-in door glass version. See D0ZZ-6521762-A for the 1970 bolt-in door glass version.
If you are swapping out a door on a 69 or a 70 don't forget that the door glass is different between the years and, if you have to swap out the glass, you will need to make sure you have the correct version of this part for the type of glass on your car (bolt-on or glue-on) or your door glass height, when all the way down, will be off.
There is now a reproduction of this part, but be aware that it is about a 1/8" taller than the originals, so the window will not roll down quite as far as it will with an OEM bumper.
Ford part # C9ZZ-6521762-A.
Do you have questions about Glue-In vs Bolt-In glass? How about how to properly install Glue-In glass in your 1969 Cougar or Mustang? Check out our video below for some great glassy information!