Filter Funnels With Clamp are used to measure and concentrate particulate in a fluid sample onto a membrane filter or to purify the filtrate. Our funnels are of rugged construction and have a very long service life. these clear funnels have internal helicoid ribs to increase the filtration speed. Vertical outer ribs prevent airlock. Made from autoclavable plastic resin, these funnels are unaffected by corrosive liquids and are heat resistant.