The Unicel FS-2003 Swimming Pool Vertical D.E.**Filter Grid** is for up-flow and down-flow D.E. Filter systems, like American, Astral, Hayward, Jandy, Pac Fab, Premier Atlas, Purex, Sta-Rite, and Waterway. These Unicel FS-2003 filter grids are made from heavy-duty polyester and are designed to last far longer than cheaper alternatives.Unicel filter grids are made in the USA for the highest possible quality, allowing you to buy with confidence. Unicel is the nation's leading manufacturer of swimming pool filter replacement cartridges.Collar has open slot (2 notches). Length is measured from one end of the grid to the other (collar not included)Replacement for: American, Hayward, Pac-Fab 7 full + 1 partial set36 sq. ft.**NOTE: PLEASE MAKE SURE THAT YOU HAVE SELECTED THE CORRECT SIZE FOR YOUR FILTER. THIS LISTING IS FOR THE 18" LONG GRID SET.