TUF-TITE 20" Riser Domed Lid seals to the riser with a molded-in lid gasket to assure a watertight seal every time. The lid is secured with eight stainless steel screws and a horizontal screw to assure safety. This is a strong lid that is very attractive. 20-RISL-GREEN Stainless Steel Screws Included Molded-in Gasket - no more fighting with O-rings