The anodized aluminum clamp secures the membrane between the funnel and glass base. The 47mm holder is the standard size for microbiology and uses a 47mm filter membrane. Glass filter holder assemblies for the microanalysis of liquids for biological or particulate contamination under vacuum. While the sintered glass frit support base can be used for general filtration, the 304 stainless steel screen(w/ PTFE gasket) is recommended for viscous or proteinaceous solutions to maximize flow rate and the screen ensures particles will not be shed into the filtrate. The PTFE support can filter acidic solutions at a higher flow rate.