a blow - molding installation for manufacturing receptacles from blanks of thermoplastic polymer , said installation comprising a bell - nozzle for blowing a fluid under pressure into a blank disposed in a cavity of a mold , the end of the nozzle being in the shape of a bell which is suitable , during blow - molding , for being pressed into leaktight end - to - end abutment against a wall of the mold while capping the neck of the blank that emerges from said wall ; said installation further comprises means for securing the nozzle to the wall of the mold by mutual attraction , which means can be activated , after the nozzle has been brought into end - to - end contact with the wall of the mold without flattening a sealing gasket , so as to attract the nozzle and the wall towards each other with an attraction force greater than the repulsion force due to the pressure of the blow - molding fluid .