an improved replaceable filtration unit for high viscosity fluids , of the self sealing semi - disposable type and having inert granular material supported by a screen within a housing , wherein the improvement comprises having the screen &# 39 ; s rim swaged into the housing , preferably with an interference fit within the range 0 . 005 to 0 . 015 inches . the invention improves the performance of packs used to filter and extrude molten polymer into shaped articles .