Abstract: A blow tube unit includes a retainer insert assembly with a restrictor and an injector blow tip. The restrictor includes restricting means to prevent the communication of a thermosetting fluent material from a reservoir to a sand core mold in the absence of blow cycle pressure. Constructed from a single block of metal, the restrictor is detachably secured to a lower portion of the blow tube unit in order to allow for removal and cleaning. The injector blow tip is made from an elastomeric material and is detachably secured to a lower portion of the restrictor.