NDS D109-PL 6" in. Round Valve Box Cover (COVER ONLY) for reclaimed water. NDS 6" in. round valve valve boxes and covers are injection molded of recycled polyolefin material with a melt index between 10-12. Coloring and UV stabilizers are added, alon gwith processing lubricants when needed. The 6" in. round cover shall have an average thickness of .150".