10 Year Life These certified unblockable main drain covers are superflow rated and their design provides comfort under foot. These covers are easy to install and no special tools are needed. Also, there is no complicated retrofitting required. Select Grate Size Above MLD-FGD-0909-2W - 9” Square cover and frame, white Open area 42.12 sq. in. Wall flow: 248 gpm Floor flow: 261 gpm MLD-FGD-1212-2W - 12” Square cover and frame, white Open area 81.30 sq. in. Wall flow: 340 gpm Floor flow: 365 gpm MLD-FGD-1818-2W - 18” Square cover and frame, white Open area 183.06 sq. in. Wall flow: 712 gpm Floor flow: 816 gpm