Abstract: A mold for producing thermoplastic pieces by blow process, which pieces are used for storing liquid and solid materials, having two equal symmetrical parts (1) and (1'), each of which is formed by a vertical plate (2) and provided with extensions (3), adjacent the upper and lower edges of the plate (2). Screws (4) which are screwed into holes (5), provided in one lateral edge of another plate (6), and is allowed to slide along channels (7); the plate (2) is provided with a slit (8) through which the screw (9) passes over plate (6) and is screwed into the hole (10) provided on another plate (11) which is orthogonal to plates (2) and (6).