Engineered with compression spring operators to provide smooth, easy, one-hand operation. Automatic hold-open arm locks the cover in the open position to ensure safe egress. Overlapping cover design, full welded corners on cover and curb, EPDM rubber gasket, and fully insulated cover and curb ensure weathertightness and energy efficiency. Constructed with corrosion resistant materials to provide many years of trouble free, dependable service. Heavy gauge construction and positive latching mechanism maintain building security. Curb features the Bil-Clip® flashing system, an innovative method to quickly and easily secure single-ply roofing material to Bilco roof products. Designed for installation over a service stair.