Not sure what you mean. Tank is 18" wide. At the top of the tank, across the 18" width is a piece of glass added as support. When trying to hang the typical overflow tank, the "U" shape that hangs over the side of the tank does not fit over the brace
A
__
l l l
l l ___ l l l
TANK l l l <overflow
l l____l
l
The width of "A" needs to be 2 3/4 inch. Typical overflow is about 1 1/2 inches.