I was driving my Ford F150 and when I got home I noticed a grey plastic piece on floor mat can someone tell me what it is and where it goes?

You can view an image if the plastic piece at http://s1174.photobucket.com/user/Justinamazing1888/library/?view=recent&page=1

No clue. Looks like a cover piece where a fastener sits. Put it in the console box and ask a mechanic when your truck is due for maintenance.

If the piece is larger than in the photo, best guess is that it fits around steering column… Only way to know is look under the dash

Seat-belt retainer cover.