Select Grate Size or Additional Hardware Above SG640-4790V - 9” Square cover and frame Open area 43.60 sq. in., Flow rate: 203 gpm @1.5 ft/sec. Wall flow: 208 gpm @1.59 ft/sec. Floor flow: 289 gpm @ 2.33 ft/sec. SG640-4720V - 12” Square cover and frame Open area 62.40 sq. in. Flow rate: 292 gpm @1.5 ft/sec. Wall flow: 280 gpm @1.44 ft/sec. Floor flow: 356 gpm @ 1.83 ft/sec. 640-4770 V - 18” Square cover and frame Open area 174.40 sq. in. Flow rate: 812 gpm @1.5 ft/sec. Wall flow: 517 gpm Floor flow: 788 gpm @ 1.09 ft/sec. 819-1031 - Additional Hardware #8 x 1 Stainless steel screw