A blow-molding mold assembly comprising: a base mold cavity located within the mold-holder of a molding machine, characterized in that the assembly includes an interchangeable insert located within the base mold cavity; the base mold cavity having in its left side a gliding locking means and in its right side having fixed locking means, and the interchangeable insert having in its left and right sides grooves to receive the locking means corresponding to each side of the base mold cavity to avoid rotational movement of the interchangeable insert, the interchangeable insert having further an exterior edge to be housed in an interior recess of the base mold cavity to avoid longitudinal movement of the interchangeable insert.