It basically acts as a spacer, because the factory manifold studs have spacers on them that do not allow you to pull the H-pipe onto the manifold completely and you will be greeted with a 'tick, tick, tick' exhaust leak.
You can throw the spacer away, and replace your header studs with Napa part number 600-1819 - It comes with two new studs (no spacers) and two new nuts. About $7.
It is the factory part for the Ford Taurus, but bolts right in...