Replacement septa are not offered for all cap types and sizes, as manual assembly is not recommendable due to contamination risk and possible wrong side orientation. Nevertheless, for the most common sizes and septa materials we offer them. Please consider that the nominal diameter of the septa sometimes might be smaller than the ND of the cap due to the cap's wall thickness (e.g. N 17 septa are asembled into magnetic N 18 screw caps).