Type AA (0.8 µm) and HA (0.45 µm) MF-Millipore™ membrane filters, matched in pairs to within ± 0.1 mg, are available in 37 mm (AA) and 47 mm (AA and HA) diameters. Used for gravimetric analysis of particle contamination by the matched-weight filter method, these products eliminate the need to preweigh the test filter.