GR121 Filter Paper Circles. 100 Circles/PK. 2.40cm diameter circles. Glass Fiber, Binderless Filter Paper. Medium filtration speed & absorbence. Weight 142g/m2, Thickness 0.66mm, Herzberg 152sec/100ml, Rapidity 45ml/min, Capillary Rise 50mm, Retention 1.0um, Frazier Air Flow 2.3cfm/ft2.