These PYREX^® Buchner funnels have a coarse porosity fritted disc with a porosity range of 40 to 60µm which is held toward the maximum pore diameter. The porosity for the pore diameter of the filter is determined in the same manner as specified in ASTM E-128 “Maximum Pore Diameter and Permeability of Rigid Porous Filters for Laboratory Use.” The disc should not be subjected to pressure differential in excess of 1 atmosphere. The top edge is beaded.