Whatman 10463607 ReZist, 50mm Dia, 0.2 micrometer Pore Size, PTFE, Sterile, 10/pk (PN:10463607)

REZIST 50/0.2 PTFE S 10/PK
ReZist™ 50 mm Syringe Filter, PTFE, 0.2 µm, (Sterile), 10/pk is particularly suitable for protective vents and for in-line filtration and isolation applications. 

Also, check out the Ahlstrom 0540-1850 Quantitative Filter Paper, Grade 54, 185 mm