AquaStar Pool Products 18MF103 MoFlow Square Mud Frame with Suction Outlet Cover; 18 Inch, UV-Resistant Engineered Polymer, Light Gray is designed to replace standard 18" square 2 x 2 grid cover assemblies that have four 9" square covers with 8 1/4" center-to-center screw hole measurement with 3/4" deep existing frames. Manufactured from superior UV-resistant engineered polymers. Replace the drain cover every five years from the date of installation.