Is this the right overflow box?
Tenecor wall mount overflows are intended for installation on a single flat surface such as the tank's back or side wall. When mounted to a side wall, the aquarium can be viewed unobstructed from three sides as in a room divider set up. This is a CLOSED BOTTOM overflow which means it does not need to be sealed to the bottom of the aquarium.
The bird's nest design allows you to adjust the mounting height as desired.
A siphon tube or wall drill thru is required for these types of overflows.
Dimensions are LxWxH where "W" is the distance from the front of the box to the aquarium wall.
Water inlet slots are approximately 1/4 inch wide and extend down approximately 1-1/2 inches from the top of the box. Keep in mind your water level will generally be at the bottom of the overflow slots.