J.w. Winco 741-40-g1-as-2 aluminum plug with drain symbol with 2mm vent hole – g 1″ pipe thread the seal is retained in a groove undercut in the mating face, which prevents it from dropping out and from extruding when the plug is tightened. For this reason the seal can be of a softer material which offers better sealing. Nbr seal: maximum heat resistance: 120c (250f).