Fuel filter for Portable Buddy heater (Item no.173690) and Big Buddy (Item no.173635) heater. Due to contaminants found in propane tanks and propane hose assemblies, Mr. Heater strongly recommends the fuel filter be used any time the Portable Buddy or Big Buddy are used with a 20 lbs. to 40 lbs. propane cylinder. For use with Mr. Heater Big Buddy or Portable Buddy heatersRecommended when using F273701 or F273702 hosesAttaches directly to heaterKeeps contaminants from entering heater