a molding device for the production of containers in thermoplastic material by blowing or blow - drawing , including a mold with two mold halves mutually mobile and provided with a locking device with first and second lock elements , in the form of catches , extending over the whole height of the respective mold halves and a projecting wing on one mold half , including a rotation surface on which a mobile piece is applied over the whole height thereof which includes the second lock element , such that , on blowing , the forces are taken by said mobile piece over the height of the mold by means of the rotation surface .