A mounting box comprising: a longitudinal centre axis (X-X), a bottom part comprising a bottom portion and a connection portion, said bottom part forming a bottom of the mounting box and being provided with at least one pre-prepared point (18A, 18B) for a tube and/or cable lead-in, a separate top part (20, 30) being connectable to the bottom part, the top part (20, 30) being formed of a tubular body portion (21, 31) with a first end (21A, 31A), the bottom part and the top part (20, 30) are connected to each other through first connection means positioned in connection with the bottom part and second connection means positioned in connection with the top part (20, 30), the first end (21A, 31A) in the tubular body portion (21, 31) in the top part (20, 30) is provided with radially outwardly from the body portion (21, 31) extending flange means (22, 32), and fastening means (220, 230) cooperating with the flange means (22, 32) in order to fasten the mounting box to a wall, the bottom part is adapted to be pushed in the axial (X-X) direction at least partly into the top part (20, 30) so that an opening is formed through the body portion (21, 31) into a mounting space formed in the interior of the mounting box, characterized in that the first connection means comprises radially directed grooves being positioned axially X-X consecutively on an outer surface of the bottom part and a radially outwardly directed first notch on an outer end of the bottom part, the second connection means comprises a second radially inwardly directed notch on an outer end of the top part, whereby a snap locking is achieved between the bottom part and the top part when the second notch of the second connection means seats into a respective groove on the first connection means so that the axial (X-X) position of the bottom part can be varied in relation to the top part in order to vary the axial (X-X) length of the mounting box between a maximum axial length and a minimum axial length. a longitudinal centre axis (X-X), a bottom part comprising a bottom portion and a connection portion, said bottom part forming a bottom of the mounting box and being provided with at least one pre-prepared point (18A, 18B) for a tube and/or cable lead-in, a separate top part (20, 30) being connectable to the bottom part, the top part (20, 30) being formed of a tubular body portion (21, 31) with a first end (21A, 31A), the bottom part and the top part (20, 30) are connected to each other through first connection means positioned in connection with the bottom part and second connection means positioned in connection with the top part (20, 30), the first end (21A, 31A) in the tubular body portion (21, 31) in the top part (20, 30) is provided with radially outwardly from the body portion (21, 31) extending flange means (22, 32), and fastening means (220, 230) cooperating with the flange means (22, 32) in order to fasten the mounting box to a wall, the bottom part is adapted to be pushed in the axial (X-X) direction at least partly into the top part (20, 30) so that an opening is formed through the body portion (21, 31) into a mounting space formed in the interior of the mounting box, characterized in that the first connection means comprises radially directed grooves being positioned axially X-X consecutively on an outer surface of the bottom part and a radially outwardly directed first notch on an outer end of the bottom part, the second connection means comprises a second radially inwardly directed notch on an outer end of the top part, whereby a snap locking is achieved between the bottom part and the top part when the second notch of the second connection means seats into a respective groove on the first connection means so that the axial (X-X) position of the bottom part can be varied in relation to the top part in order to vary the axial (X-X) length of the mounting box between a maximum axial length and a minimum axial length.