This lid is designed to fit most standard septic risers and also Tuf-Tite manufactured risers. This lid is flat on top. Domed lid versions are also available. Features a molded-in lid gasket which assures a watertight seal every time. No fighting with O-rings. This lid can be filled with concrete on the underside to add additional weight and security. Designed specifically to fit 20" Diameter Tuf-Tite products ONLY. Tuf-Tite makes a full line of risers and accessories for pre-cast applications. When aligned properly, the Screw holes will ALWAYS line up.