Designed for on-site calibration, the all-metal type water dam of this 15-1/4" (390) diam. corrosion resistant Duco coated cast iron drain can be adjusted to block drainage of standing water a minimum of 2-1/2" and a maximum of 5" on flat roofs where a rooftop pool of water is retained to insulate the building's interior. This drain is also perfect for installation as a safety overflow drain in conventional roofs. To protect the drainage system, a Duco cast iron dome strainer holds debris at bay.