The invention relates to a moulding system (3), in particular a calibration die (17), for an extrusion plant, with preferably parallel inlet and outlet faces (28, 29) spaced at a distance apart and with side faces (30, 31, 32, 33) extending between them. A longitudinal axis for the object to be fed through a calibration orifice (24) is disposed substantially perpendicular to the inlet and outlet face (28, 29). Provided between a shaping surface (25, 26) and a side face (30, 31, 32, 33) is a gap (37, 38) extending at least across a part of the distance between the inlet and outlet face (28, 29). The gap (37, 38) is disposed between several immediately adjacent parts of several shaping surfaces (26) of the calibration orifice (24) and at least one of the side faces (30, 31, 32, 33). At least the parts of the shaping surfaces (26) co-operating with the gap (37, 38) are displaceable relative to the other shaping surfaces (25).