NDS 6" black square structural foam polyolefin grate is a 6" black square grate with a diagonally converging pattern and uv inhibitors. it has an open surface of 10.40 sq.in. and a flow rate of 13.62 gpm. it fits 3" or 4" sewer and drain pipe, 3" or 4" corrugated pipe, and 3" or 4" triple wall pipe. it can withstand loads of 1-60 psi and is recommended for pedestrian, bicycle, and wheelchair traffic. it comes with a limited lifetime warranty.