its lower position to its upper position these two means are very similar and have two identical mechanisms 38 on which a specific tool is adapted for controlling the raising or lowering the common mechanism 38 is illustrated in perspective in fig3 and in cross section in fig4 in fig4 also illustrated is a push tool 40 specific to controlling the descent in order to ensure the gripping of the preform 10 the mechanism 38 has a frame 42 which is intended to be attached to the body of the oven on this frame 42 a bracket shaped arm 44 is mounted so as to be able to slide along the gripping direction that is in this instance in the vertical direction to do this a sliding connection is used formed by a vertical rail 46 integral with a vertical upright 50 of the bracket 44 and by a slide 48 attached to the frame 42 the mechanism has means to cause an alternating movement of the bracket 44 along the axial direction of gripping in the proposed example a system of a connecting rod 84 and crank 86 is used driven by a rotary electric motor 88 in the horizontal axis of course any other known means to produce an alternating axial movement of the bracket 44 can be used thus the movements.