This is a horizontal 4-sided overflow that fits at the top center of the reef tank, usually on the back wall.  

L x W x H: 12" x 4" x 5" (internally 11.5" x 3.75" x 4.75" tall)

Second Picture: With a lid to prevent algae from growing in the box. Lids are $12 extra.

For custom sizes or requests, email me.