Dropped pan, found this.
I had one of those in the transmission pan of a 1970 Mustang. I was told that it was a dipstick tube plug that the factory uses in the automatic transmissions, so it is nothing to worry about. I guess they are supposed to pull them out to install the dipstick tube, but apparently sometimes they must push them in to the pan. You can discard the part if you wish, it is not needed.