A auxiliary constructional component includes a base member (11), a guide section (12) for a fastening element (30) and projecting from the base member (11), and a feeler element (20) displaceably supported on the base member (11) for displacement along an attachment axis (A) defined by a through-opening (13) formed in the guide section (12), having at least one, radially spaced from the through-opening (13), placement surface (21) for a press-on feeler (42) of a setting tool, and projecting in an initial position of the feeler element (20) beyond a side of the base member (11) remote from the guide section (12).