A fastener is provided for projection resistance welding to a panel. The fastener includes a base having a fastening element, such as a threaded stud or a nut integral therewith. Multiple projections formed integral with the base extend therefrom to engage with the panel to be welded to the panel by electric resistance welding. A groove is provided in the base facing the panel and is filled with a heat activated expandable sealer material. Upon heating of the base during the electric resistance welding, or in an oven, the sealer expands to fill and seal any gap between the base and the panel.