That glass brace is actually the support memeber on those tanks (I'm thinking it is an oceanic right). If you take the rim off of a tank like a 55g you will have a huge mess on your hands. I would watch doing it to any tank that has a center brace built into the plastic rim it is there for a reason. I have seen full 55's bow out 2-3" when the center brace broke. Ithen shattered at the top and you know the rest. Any tank that doesn't have a center brace doesn't really use the rim for support other than to hold the hood up.