Abstract: Apparatus for filtering heat-softened plastic material under pressure of extrusion comprising a substantially continuous screen with screw means for positively moving the same past the filtering area, said screw means being located in a passage open to the fluid plastic material, with means to harden the plastic material in the passage into a nut in which the filter is embedded. The screw means also functions to prevent the solidified slug (nut) from escaping, preventing leakage.