The mount that I am talking about is the round part. It's a combination of rubber and plastic. Anyway, I've changed a few do to excessive damage caused by a jack. It's a good idea to put a piece of wood between jack and lift mount.
The pin that you took out is for the removal of mount. The body of the car has a hole in which the mount plugs in. As you push the pin in, it spreads the "anchors" and holds it firmly in place. Similar to those small gray clips that you find all over the car (ex. trunk panel clips).