This is an plastic cover that sits on top of a standard overflow box, and blocks the light (and jumping fish).
Features knock-outs for 1/2" tubes, as well as power cords or air lines. Simply grasp the tab with pliers, and snap out the piece. Save the piece, and it can be super-glued back in later if desired.
Covers can also be modified by cutting or sanding, in order to make larger or custom holes.
Aqueon Std: 10.5 x 5.2 x 0.31" (266 x 130 x 8mm )