Abstract: A hollow three dimensional metal article is formed by cutting two identical flat metal blanks, forming a hole in one of the blanks and upsetting the metal around the hole to accommodate the head of a threaded hollow stud having a sealing collar without interference when the blanks are in face contact, placing the blanks in face contact while the stud is in place, welding the metal blanks together continuously around the entire perimeter of the superimposed blanks, and forcing liquid under pressure through the hollow stud until a precise preset maximum pressure is reached to inflate the blanks to their final three dimensional form. Optional steps include cutting off the portion of the three dimensional form in which the stud and the opening for the stud are located and welding a standard fitting into the opening thus created and the provision of other portions of the three dimensional object with other attachments and fittings.