Black rubber mystery part fell out of iPhone 4 during tear down

Hi,

I just tore down my iPhone 4 in order to replace the Home button and when I peeled the front screen off a small black rubber piece fell from the phone. I do not know if it came from the screen side or the back side as I was moving the phone around when it happened. The piece is somewhat cylindrical and about 6-7 mm long and about 2 mm wide with a groove running gown the length of one side. I have looked at a number of tear down and repair pictures and have not identified where this part goes. Will try to photo the piece and post. The piece seems to a a cushion or spacer.

Thanks,

Thomas