Abstract: A mold for forming a motor vehicle part from a polymer material comprising at least one partially overmolded metal insert having a portion intended to be covered with polymer material and a portion intended to be left uncovered. The insert comprises an overmolding limit and the mold comprises a die and a punch capable of taking different positions between: an open position for introduction of inserts and polymer material in the mold, and a molding position wherein the mold cavity is closed, the mold comprising holding means and blocking area at least one movable part and at least one projection extending over a sealing area completely including the insert overmolding limit, to prevent the polymer material from crossing the sealing area seeping between the part of the insert intended to not be covered and one of the opposite faces of the holding means and of the blocking area.