An investigation to flow test and measure a large set of orifice plates to determine the proportion of existing orifice plates have measured discharge coefficients outside of the Reader-Harris/Gallagher equation 95% confidence limits. The research determined if the existing tolerance specifications adequately describe the dimensions of an orifice plate required to conform to the Reader-Harris/Gallagher equation calculated discharge coefficient. The testing also underscored the influence of manufacturing variations on orifice plate performance.