Abstract: A sheet metal plug for holes in sheet metal boxes, such as conduit holes in electrical junction boxes, includes a circular plug disc having a groove formed along a chord thereon. The plug disc is bent along the groove such that a portion of the disc is angularly displaced from the plane of the remainder thereof. A number of tabs, carried on the undersurface of the disc, are arranged to engage the edge of the hole when the plug is inserted into the hole. One of the tabs is positioned on the angularly displaced portion of the disc such that the disc is initially insertable into the hole, after which the displaced portion is straightened to bring each tab into secure engagement with the sheet metal which is being plugged. The thickness of the disc is substantially reduced along at least a portion of the groove such that its resistance to bending is substantially reduced therealong. A land or area of increased thickness bridges the groove to strengthen the disc at the groove.