STERILE Pall GN-6 Metricel Membrane Filters, 47mm diameter, 0.45um, Gridded, Pk of 200 Individually wrapped and gamma-irradiated. The GN-6 membrane is certified for the microbiological analysis of potable, waste, process, and natural waters in accordance with the Membrane Filter Technique referenced in Standard Methods for the Examination of Water and Wastewater.