US Patent 8418812 Ribbed drain plug

A drain hole sealing system has a ribbed drain plug that includes a shaft for engaging the drain hole of a fluid container, a head portion for engaging a tool, and at least one annular rib or ridge or projection extending from the head portion in the same direction as the threaded shaft and concentric therewith. The annular rib or ribs provide compressive and biting engagement with an annular deformable seal positioned concentrically around the drain hole that is engaged by the shaft of the drain plug. At least one annular rib moves into biting engagement with the annular deformable seal so that the seal deforms at least partially around the annular rib when the drain plug is tightened.