6 inch extension for NDS 117 series 13 inch x 20 inch Jumbo valve box. Made from quality material for longevity. Designed for the professional contractor and heavy-duty use and offer superior strength for non-residential and utility applications. Competitive Benefits Thicker wall dimensions for increased strength and durability, Reinforced covers for heavier loads, Reinforced ribs offer exceptional sidewall strength, Overlapping covers prevent dirt and grass from settling between body and cover.