The adapter you reference is called a "Street Ell". They are indeed both the same size, 1/8" NPT. I would keep it and I'll tell you why. When I received my Genesis 1000LX, it had a cracked street ell where is gas line screwed into it. I'm sure this happened from over tightening. It's a lot easier and much cheaper, ($2.00), to replace a cracked ell than a cracked manifold. Weber does not call it out as a separate part but rather considers it as part of the manifold assembly. Given the extra expense of both the part and installing it, I have a hunch hey had a very good reason for offering it and have a hunch over tightening may have been why.