The plunger (1) has a cylindrical housing (2) axially protruded below a roller (4) by an arch piece (6). A lower side (8) of the piece is turned towards an output-sided forehead (7) of the housing. An upper side (9) of the piece includes a shell-like form (10) in which a movable shell segment (12) separated from a ring is placed. The roller is supported on an inner rail (13). The segment runs in the shell-like form. An axial guiding column (14) is arranged at an inner sheath of the housing. The segment is arranged at a separation forehead over a corner recess in a turnout-protected manner. The shell segment is formed as a half shell, a one-third shell or a quarter shell. The housing is formed as steel sheet- and/or extrusion parts.
