Oregon 55-821 Black String Trimmer Bump Head Knob Attachments Oregon 55-821 Replacement Trimmer Bump Head Knob (black) Fits E-Z Line Advance systems with 5/16 - 18 RH thread Fits Homelite models ST155, ST165, ST175, ST285, SX135, GST-18, HLT-15, HGT, ST185BC, ST275 & GST Replaces Homelite DA98866A