Abstract: A molding flask structure for molding close tolerance articles, such as prosthetic dental devices. The flask structure includes upper and lower flask members that each include cup-recesses adapted to face each other to define therebetween a mold cavity when the flask members are connected together. Assembly of the flask members is effected by a plurality of connecting bolts to securely hold the flask members together. Vent passageways are provided in the flask members to extend from the mold cavity to permit excessive internal pressures to be relieved to the exterior of the flask member. A sprue opening defined by semi-cylindrical recesses in contacting faces of each of the flask members extends from the mold cavity to the exterior to permit the introduction of molding material into the mold cavity. The sprue opening is partially threaded and partially unthreaded.