Qualitative Filter Paper - 6171-2020 - Grade 617, 50.80cm x 50.80cmAhlstrom Munksj 6171 35 m, Fast Speed This is an extremely fast filtering grade and has a larger particle retention than Grade 631. Grade 6171, a thicker filter paper with higher loading capacity, is used for rapid filtration of coarse particles and gelatinous precipitates such as in oils and resin solutions. Grade 6171 is also found in construction product testing and is used by students to retain large flocculents and precipitates.