This is one of the 2 grid sizes used in the Splash Pak DE 55 filter. 4 of the 8-1/2" wide and 2 of the 7" wide grids are used in each filter.
This is flat, with a round black connection tube about
1" in diameter running top to bottom, close to the center. The body consists of a plastic frame about 7/16" thick with filter material attached on the outside. The dimensions shown are for the plastic frame, so the actual measurements of the grid will be slightly larger.