Abstract: An automobile decklid pop-up bumper for assembly with an apertured workpiece, such as the framework of an automobile engine compartment having an aperture and a helical internal marginal portion defined around the aperture, includes a housing with an enlarged end portion for engaging the automobile hood and a shank portion extending from the enlarged end portion adapted to be received through the aperture. The shank portion has a helical thread for threadingly engaging the helical marginal portion around the aperture when the bumper is assembled with the workpiece. The housing has an axial bore with a portion of reduced radius within the enlarged end portion. The portion of reduced radius defines a shoulder.