12" x 12", Sand, Square Grate, Made Of Structural Foam Polyolefin With UV Inhibitors, Open Surface Area Is 50.76 SQIN, A Flow Rate Of 66.50 GPM, Use With The 12" x 12" Catch Basin Series, Class B Load Rated Which Is Recommended For Medium Duty Pneumatic Tire Traffic, Autos & Light Trucks At Speeds Less Than 20 MPH.