NDS 1811 18" Black Plastic Square Catch Basin Drain Grate fits on top of the 18 in. high-volume Catch Basin Drain to manage heavy flows from lawns, landscaped areas, parks, driveways, and courtyards. The 18x18 outdoor drain grate, also known as a drain cover, is made of high-density polyethylene (HDPE), treated with UV inhibitors. Fits 18 in. square catch basins, risers, and square low-profile adapters. Hassle-free limited lifetime warranty guarantees the NDS product is free from defects—or we’ll replace it.