NDS 9" black square grates are one piece injection molded from structural foam polyolefins for maximum strength. Ultraviolet light inhibitors are added to prevent fading and cracking from exposure to the sun. They also feature a pattern that allows the water to be captured more effectively. Fits 6" sewer and drain pipe and fittings and 6" corrugated pipe, as well as NDS 6" Spee-D basins. For loads of 1-60 PSI. Recommended for pedestrian, bicycles, & wheel chair traffic.