Temperature Fuel Control Knob (27mm shaft) for MH18B Mr. Heater BIG Buddy Portable Propane Heaters, Part #78418 Part #78418. Original Mr. Heater replacement temperature / fuel control knob for the MH18B Mr. Heater BIG Buddy Portable Propane Heaters. This knob will ONLY fit BIG Buddy heaters with the serial number MHC748000097072 and HIGHER and all CURRENT models. This knob has a 27mm OD shaft size. Please measure outside diameter of knob shaft for proper fit. For use on Mr. Heater, Heat Star, and Enerco MH18B BIG Buddy Portable Propane Heaters. (*Use Part #78018 knob for heaters with the serial number MHC748000097071 and LOWER, where the knob has a 12.5mm shaft base*.)