Something fell off my vehicle while I was driving down the freeway. Both belts are off and I can't figure out what piece is missing. There is a metal piece sticking out that is attached to the oil filter that looks like it may have held the belts together but im not sure. I thought maybe someone could help me.

SOURCE: My rearview mirror on my 1997 Lumina fell off and

Should be a small set screw on the mount to the windshield. Unscrew the set screw and it should slide right out.

SOURCE: i was changing the transmission

That is just an assembly plug. What this means is that nobody has ever had the pan off of your 14-year-old car before. These plugs are placed in the transmission fill tube hole when the transmissions are assembled. Then when the vehicle is on the assembly line, the dipstick tube is installed and the plug gets pushed into the transmission pan. This is NORMAL! Just keep it as a souvenir or throw it away and don't lose any sleep over it.