It's a freshwater aquarium. The hood is designed for a 50 long. The aquaium itself has the regular plastic rim around it, and a glass section near the middle.
The hood has four pieces of glass, two wide, two short, two plastic hinges, two plastic back pieces, two plastic handles, and a plastic "T" bar.
The "T" bar goes on the glass piece in the middle of the aquarium. Then you assemble the other pieces into two lids, by attaching the back piece to the short glass, to the plastic hinge, to the plastic handle.
When you put them all together tightly, there's about half an inch of space between the hood, and the front of the pannel, and the "T" piece slips around between the two sides in a 1/2 inch gap. The gap there is especially a problem, because if you accidentally push one of the covers sideways toward the middle of the aquarium, it falls off the lip on the outer end, and starts to fall into the water.
I'm tempted to go to the glassmaker, and just get slightly larger glass pannels, but the back pieces are getting old to, and I've cut more holes in it than I really need for my hoses and such.