Abstract: An elongated two-piece expandable sealing plug (20) that is adapted to sealingly close a marginal end portion of a hole or opening (22) provided in a body (21) broadly comprises: a cup-shaped member (23) having an annular open upper end, having an outer surface that is adapted to face toward a wall on the body surrounding the opening, and having an inner surface (38) that diverges radially outwardly in a direction toward the member upper end; and a head having an outer rim portion (25) mounted on the upper end marginal end portion of the member for rotation therewith, and having a central portion (26) arranged within, and secured to, the rim portion; wherein the member is adapted to be inserted (i.e., slidably and/or rotatively) into a marginal end portion of the body opening (FIG.