heater core done, found extra part?

[89foxbodycali]

can anyone please identify this piece of something for me, i have no idea what it is. after i put my dash back together i noticed this behind the carpet under where the heater core and box is.

 

[MRaburn]

It goes on the studs that stick through the firewall back out at the engine. It basically helps seal that area, its probably not a requirement. I just replaced ours last week in our project car. If I had just put the air box back in the car no way would I pull it back out to put that spacer back on.

 

[BlownFiveLiter]

Did you really need 3 threads about this?

http://www.stangnet.com/mustang-forums/836588-replaced-my-heater-core-have-extra-part.html
http://www.stangnet.com/mustang-forums/836589-please-help.html

 

[donald1956]

heater core replacement 1989 mustang

why cant firewall be cut a little to replace heater core in 1989 ford mustang and then replace heater core and put another piece of metal on there and bolt it in