A filter includes a casing enclosing a filter cartridge and a removable collection bowl. The filter cartridge includes a filter media ring with upper and lower end caps. The lower end cap of the filter cartridge has a ring-shaped member projecting axially downward. The ring-shaped member has an annular...http://www.google.de/patents/US6139738?utm_source=gb-gplus-sharePatent US6139738 - Cartridge filter with integrated threading having anti-rotation feature
