In this study, improvement of manufacturing efficiency was investigated by conducing optimizations on the design and production of 1/2 '', 3/4 '', 1 '', 11/2 '', 2 '' fittings which are widely used in the oil and natural gas pipe lines. Manufacturing processes and inspections were carried out according to TS EN 10242 standard dimensions. Factors which affect the production efficiency are analyzed by using cause and effect diagram. As a result of the investigations, it was determined that the products are averagely 12% heavier than standards and some errors were found at the placement of models. It was observed that, 300x400 flask system does not pertain for the for the fittings production. Besides, it was seen that runner weight is too much and runner gate is imperfect. For the solution of these problems, errors which are created by manufacturing methods were studied. After these studies, a new method of production was developed in order to perform an optimization. Also, layout parameters of fittings on the models were expressed with mathematical formulas. With the obtained information, it was detected that the best result was attained from 420x500 flask system. As a result of this method,1/2 '', 3/4 '', 1 '', 11/2 '', 2 '' fittings which are mass produced at the company were reviewed and adjusted. Thus, 90% of the production was optimized. Overall weights of scrap were reduced to 118,496 kg from 246,660 kg. Amount of error is decreased by shaping of products due to TSE standards and weights of products were decreased by 8-20%. New flask system took support of patent form TUBITAK and it was found suitable for patent in Russia with the name of "Flask model of fittings"(Patent nu: 2013/00806).