Flanges are used on equipment for the nozzles and in piping systems. The flanges are bolted together with a gasket in between to prevent leackage. The dimensions of flanges in piping systems and also the smaller flanges on equipment are standardized. Equipment such as pressure vessels can also have so-called body flanges. These flanges are specially made for the diameter of the equipment and are designed and calculated individually.
Below figure gives the dimension legenda as used in the table for flange dimensions.